Reverse a binary tree to satisfy the ego of a L2 Google engineer

reverst_tree_interview.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
def reverse_tree(tree):
    if tree is None:
        return
    if tree.left is None and tree.right is None:
        return
    if tree.left is None:
        tree.left = tree.right
        tree.right = None
        reverse_tree(tree.left)
    elif tree.right is None:
        tree.right = tree.left
        tree.left = None
        reverse_tree(tree.right)
    else:
        tmp = tree.left
        tree.left = tree.right
        tree.right = tmp
        reverse_tree(tree.left)
        reverse_tree(tree.right)