Subtree of another tree

/***************************************************
  Following is the TreeNode Structure

template <typename T>
class TreeNode {
   public:
    T val;
    TreeNode<T>* left;
    TreeNode<T>* right;

    TreeNode(T val) {
        this->val = val;
        left = NULL;
        right = NULL;
    }
};

*****************************************************/
bool issame(TreeNode<int> *T, TreeNode<int> *S)
{
    if(T == NULL && S == NULL)
    {
        return true ; 
    }
    else if(T == NULL || S == NULL){
        return false;

    }
    
     if(T->val != S->val)
    {
        return false ; 
    }  

    bool a = issame(T->left , S->left) ;
    bool b = issame(T->right , S->right) ;
    return a && b ; 
}
bool isSubtree(TreeNode<int> *T, TreeNode<int> *S)
{
    if(T == NULL)
    {
        return false ; 
    }
    if(T->val == S->val )
    {
        bool x =  issame(T , S) ; 
        if(x == true)
        {
            return true ; 
        }
    }
    bool a = isSubtree(T->left , S) ;
    bool b = isSubtree(T->right , S
    ) ;
    return a || b ; 
    
    // Write your code here.
}