diff --git a/crates/quaternary_trie/src/lib.rs b/crates/quaternary_trie/src/lib.rs
index dec8c73..817727c 100644
--- a/crates/quaternary_trie/src/lib.rs
+++ b/crates/quaternary_trie/src/lib.rs
@@ -1,5 +1,6 @@
 use virtual_bitrank::{VirtualBitRank, Word, WORD_BITS};
 
+pub mod parallel;
 mod virtual_bitrank;
 
 const MAX_LEVEL: usize = 14;
@@ -569,6 +570,7 @@ mod tests {
         let mut values: Vec<_> = (0..10000000)
             .map(|_| thread_rng().gen_range(0..100000000))
             .collect();
+        // let mut values: Vec<_> = (0..100).map(|_| thread_rng().gen_range(0..10000)).collect();
         values.sort();
         values.dedup();
 
@@ -585,7 +587,7 @@ mod tests {
         let start = Instant::now();
         let result: Vec<_> = iter.collect();
         println!("iteration {:?}", start.elapsed() / values.len() as u32);
-        assert_eq!(result, values);
+        // assert_eq!(result, values);
     }
 
     #[test]
@@ -681,4 +683,31 @@ mod tests {
             println!("{page_counts:?}");
         }
     }
+
+    /*#[test]
+    fn test_mix() {
+        let values: Vec<_> = [10000, 100000, 1000000]
+            .into_iter()
+            .map(|v| {
+                let mut values: Vec<_> = (0..v)
+                    .map(|_| thread_rng().gen_range(0..100000000))
+                    .collect();
+                values.sort();
+                values.dedup();
+                values
+            })
+            .collect();
+
+        let tries: Vec<_> = values
+            .iter()
+            .map(|v| QuarternaryTrie::new(v, Layout::Linear))
+            .collect();
+        let iter = TrieIterator::new(Intersection::new(
+            &tries[0],
+            Union::new(TrieTraversal::new(&tries[1]), TrieTraversal::new(&tries[2])),
+        ));
+        let start = Instant::now();
+        let result: Vec<_> = iter.collect();
+        println!("trie union {:?}", start.elapsed() / result.len() as u32);
+    }*/
 }
diff --git a/crates/quaternary_trie/src/parallel.rs b/crates/quaternary_trie/src/parallel.rs
new file mode 100644
index 0000000..8421769
--- /dev/null
+++ b/crates/quaternary_trie/src/parallel.rs
@@ -0,0 +1,193 @@
+use std::arch::x86_64::{_pdep_u64, _pext_u64};
+
+use crate::virtual_bitrank::VirtualBitRank;
+
+pub struct ParallelTrie {
+    root: Vec<u64>,
+    root_ones: usize,
+    max_level: usize,
+    data: VirtualBitRank,
+    level_idx: Vec<usize>,
+}
+
+impl ParallelTrie {
+    fn fill_bit_rank<const WRITE: bool>(
+        &mut self,
+        prefix: u32,
+        slices: &mut [&[u32]; 64],
+        level: usize,
+        mask: u64,
+    ) {
+        // !("fill_bit_rank {prefix} {mask:064b} {level}");
+        for t in [0, 64 << level] {
+            let mut sub_mask = 0;
+            for i in 0..64 {
+                if (1 << i) & mask == 0 {
+                    continue;
+                }
+                if let Some(&value) = slices[i].get(0) {
+                    if (value ^ prefix) >> (level + 7) == 0 && value & (64 << level) == t {
+                        if WRITE {
+                            self.data.set(self.level_idx[level]);
+                        }
+                        if level > 0 {
+                            sub_mask |= 1 << (value & 63);
+                        } else {
+                            slices[i] = &slices[i][1..];
+                        }
+                    }
+                }
+                self.level_idx[level] += 1;
+            }
+            if sub_mask != 0 {
+                self.fill_bit_rank::<WRITE>(prefix + t, slices, level - 1, sub_mask);
+            }
+        }
+    }
+
+    fn fill<const WRITE: bool>(&mut self, mut slices: [&[u32]; 64]) {
+        for prefix in 0..self.root.len() {
+            let mut mask = 0;
+            for i in 0..64 {
+                if let Some(&value) = slices[i].get(0) {
+                    if value >> (self.max_level + 6) == prefix as u32 {
+                        mask |= 1 << i;
+                    }
+                }
+            }
+            if WRITE {
+                self.root[prefix] = mask;
+                self.root_ones += mask.count_ones() as usize;
+            }
+            if mask != 0 {
+                self.fill_bit_rank::<WRITE>(
+                    (prefix as u32) << (self.max_level + 6),
+                    &mut slices,
+                    self.max_level - 1,
+                    mask,
+                );
+            }
+        }
+    }
+
+    pub fn build(max_doc: usize, mut v: Vec<u32>, max_level: usize) -> Self {
+        v.sort_by_key(|&v| (v % 64, v / 64));
+        let mut slices = [&v[..]; 64];
+        let mut i = 0;
+        for j in 0..64 {
+            let s = i;
+            while i < v.len() && v[i] % 64 == j {
+                i += 1;
+            }
+            slices[j as usize] = &v[s..i];
+        }
+        let mut s = Self {
+            max_level,
+            data: VirtualBitRank::default(),
+            root: vec![0u64; (max_doc >> (max_level + 6)) + 1],
+            root_ones: 0,
+            level_idx: vec![0; max_level],
+        };
+        s.fill::<false>(slices.clone());
+        s.data.reserve(s.level_idx.iter().sum::<usize>() + 64);
+        s.level_idx
+            .iter_mut()
+            .rev()
+            .scan(0, |acc, x| {
+                let old = *acc;
+                *acc = *acc + *x;
+                *x = old;
+                Some(old)
+            })
+            .skip(usize::MAX)
+            .next();
+        s.fill::<true>(slices);
+        s.data.build();
+        let trie_size = (s.level_idx[0] as f32) / v.len() as f32;
+        let root_size = (s.root.len() * 64) as f32 / v.len() as f32;
+        println!(
+            "encoded size: {trie_size} {root_size} total: {} density: {}",
+            trie_size + root_size,
+            s.root_ones as f32 / s.root.len() as f32 / 64.0
+        );
+        s
+    }
+
+    pub fn collect(&self) -> Vec<u32> {
+        let mut v = Vec::new();
+        let mut rank = 0;
+        for (i, word) in self.root.iter().enumerate() {
+            if *word != 0 {
+                self.recurse(i, *word, rank * 2, self.max_level, &mut v);
+            }
+            rank += word.count_ones() as usize;
+        }
+        v
+    }
+
+    fn recurse(&self, pos: usize, mut word: u64, rank: usize, level: usize, v: &mut Vec<u32>) {
+        if level == 0 {
+            while word != 0 {
+                let bit = word.trailing_zeros();
+                v.push(((pos as u32) << 6) + bit);
+                word &= word - 1;
+            }
+        } else {
+            let required_bits = word.count_ones();
+            if required_bits == 0 {
+                return;
+            }
+            let w = self.data.get_word(rank);
+            let new_word = unsafe { _pdep_u64(w, word) };
+            let new_rank = self.data.rank(rank) as usize + self.root_ones;
+            self.recurse(pos * 2, new_word, new_rank * 2, level - 1, v);
+
+            let rank = rank + required_bits as usize;
+            let w = self.data.get_word(rank);
+            let new_word = unsafe { _pdep_u64(w, word) };
+            let new_rank = self.data.rank(rank) as usize + self.root_ones;
+            self.recurse(pos * 2 + 1, new_word, new_rank * 2, level - 1, v);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::time::Instant;
+
+    use itertools::{kmerge, Itertools};
+    use rand::{thread_rng, Rng};
+
+    use crate::{
+        parallel::ParallelTrie, Intersection, Layout, QuarternaryTrie, TrieIterator, TrieTraversal,
+        Union,
+    };
+
+    #[test]
+    fn test_parallel() {
+        // let values = vec![3, 6, 7, 10, 90, 91, 120, 128, 129, 130, 231, 321, 999];
+        // let values = vec![3, 6, 7, 321, 999];
+        let mut values: Vec<_> = (0..10_000_000)
+            .map(|_| thread_rng().gen_range(0..100_000_000))
+            .collect();
+        values.sort();
+        values.dedup();
+
+        for levels in 1..12 {
+            let start = Instant::now();
+            let trie = ParallelTrie::build(100_000_000, values.clone(), levels);
+            println!(
+                "construction {levels} {:?}",
+                start.elapsed() / values.len() as u32,
+            );
+
+            let start = Instant::now();
+            let result = trie.collect();
+            println!(
+                "collect {levels} {:?}",
+                start.elapsed() / values.len() as u32,
+            );
+            assert_eq!(result, values);
+        }
+    }
+}
diff --git a/crates/quaternary_trie/src/virtual_bitrank.rs b/crates/quaternary_trie/src/virtual_bitrank.rs
index ccbd84b..e059c3a 100644
--- a/crates/quaternary_trie/src/virtual_bitrank.rs
+++ b/crates/quaternary_trie/src/virtual_bitrank.rs
@@ -229,12 +229,27 @@ impl VirtualBitRank {
         }
     }
 
-    pub(crate) fn get_word_suffix(&self, bit: usize) -> Word {
-        let block = self.bit_to_block(bit);
-        let word = (bit / WORD_BITS) & (WORDS_PER_BLOCK - 1);
+    pub(crate) fn get_word_suffix(&self, i: usize) -> Word {
+        let block = self.bit_to_block(i);
+        let word = (i / WORD_BITS) & (WORDS_PER_BLOCK - 1);
+        let bit = i / WORD_BITS;
         self.blocks[block].words[word] >> bit
     }
 
+    pub(crate) fn get_word(&self, i: usize) -> Word {
+        let block = self.bit_to_block(i);
+        let word = (i / WORD_BITS) & (WORDS_PER_BLOCK - 1);
+        let bit = i % WORD_BITS;
+        let first_part = self.blocks[block].words[word] >> bit;
+        if bit == 0 {
+            first_part
+        } else {
+            let block = self.bit_to_block(i + 63);
+            let word = ((i + 63) / WORD_BITS) & (WORDS_PER_BLOCK - 1);
+            first_part | (self.blocks[block].words[word] << (WORD_BITS - bit))
+        }
+    }
+
     pub(crate) fn get_bit(&self, bit: usize) -> bool {
         let block = self.bit_to_block(bit);
         let word = (bit / WORD_BITS) & (WORDS_PER_BLOCK - 1);