merge_two_binary_trees.py

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


class Solution:
    def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
        if root1 is None: return root2
        if root2 is None: return root1
        root1.val += root2.val
        root1.left = self.mergeTrees(root1.left, root2.left)
        root1.right = self.mergeTrees(root1.right, root2.right)
        return root1