binary search tree function using c++

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

Ex3. Get the Longest Path (25 points) Write a member function called DLList BST:: get_longest_path() that returns a DLL of the longest path in the tree. For example, the red nodes in the following tree are on the longest path and should be added to the list. In case there are multiple longest paths, retrieve any of them