#617 mergeTrees.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: Optional[TreeNode], root2: Optional[TreeNode]) -> Optional[
        TreeNode]:
        if root1 is not None and root2 is not None:
            root1.val = root1.val + root2.val
            root1.left = self.mergeTrees(root1.left, root2.left)
            root1.right = self.mergeTrees(root1.right, root2.right)
            return root1

        else:
            if root1 is None:
                return root2
            else:
                return root1