binary search tree function using c++

the question give us the doubly linked list code (#include"DLL.h" is included in the code )

Ex4. Extract SubTree (25 points) Write a BST member function BST BST:: Copy_subTree (const T& n) that will extract and return the subtree rooted at the node containing the value n. For example, on the following tree, the function should return the subtree shown to the right. The current tree The returned BST The current Tree after calling the function 12 12 n 30 2 9 30 9 14 39 14 39