Hi, below is implementation of Divide and conquer . I can't figure out what is time complexity ? O(h)??

```
int sumOfLeftLeaves(TreeNode* root) {
if (root == NULL) {
return 0;
}
int leaf = 0;
if (root->left && !root->left->left && !root->left->right) {
leaf = root->left->val;
}
return leaf + sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right);
}
```