Please write this function in python:

Rules:

TreeNode class:

4 tree_sum (root) Write a function, tree_sum(), which takes a tree as a parameter, and returns the sum of all of the values in the tree. You may assume that all of the values are numeric; an empty tree should return zero. A few of the functions will assume that the tree is a BST; however, most will not. All of the trees will be binary trees, and will use the TreeNode class that I've provided in tree_node.py . Put all of your functions into a file named tree_funcs.py Except where explicitly stated in the function descriptions below, you may choose whether to use recursion or a loop in the functions. (Note that the recursive solution will be much easier in most cases.) In this project, helper functions and default arguments) are banned. In two of the functions in this project, you may assume that the tree we pass you is not empty. But only do this if we explicitly say so! Most of your functions must handle the empty-tree case. class TreeNode: def __init__(self, val): self.val val self.left None self.right None =