Consider the partial implementation of a Binary Search Tree class. For simplicity, each Node stores only the key. Add a public member function to class BST that returns the size of the tree (i.e, the number of the nodes).(Hint: think recursion!) template class Node t T key: Node left, *right, parent: template class BST private: Node root BST: root (nullptr) // default constructor sets root to nullpt: Node *Searh (const T akey) public: Node *cur = root; while (cur != nullptr) if (keycur->key) return cur: // Found else if (key key) cur = cur->left; else cur cur->right; = return nullptr; I/ Not found int size) YOUR CODE GOES HERE