If file name is of the form tree://<ID>, the entire tree, indicating it is the root.
If file name is of the form subtree://<ID>, is the subtree, and can enable downloading speicifcally the subtree. (Is subtree required if we are using tree?)
If file name is of the form treenode://<ID>, is the tree node
There should be a variety of ways of organizing the data, and it should be kept
in sync. For example node[id] should be a map that returns the nodes, and
tree[id] should be a map that returns the trees or subtrees.
At all times the edges should be tracked and kept together, in a list or some sort.
Edges should store the entire branch length.