what is the complexity of this code
AVL_Node* search(AVL_Node* node, int key) { //***
  if (node == NULL) {
    return NULL;
  }
  if (key == node->key) {
    return node;
  }
  if (key < node->key) {
    return search(node->left, key);
  }
  return search(node->right, key);
}