leetcode 617:Merge Two Binary Tree with Python

https://leetcode.com/problems/merge-two-binary-trees 

class Solution:
    def mergeTrees(self, t1, t2):
        """
        :type t1: TreeNode
        :type t2: TreeNode
        :rtype: TreeNode
        """
        if (not t1) and (not t2):
            return None
        else:
            if (not t1) and t2:
                t1 = TreeNode(t2.val)
                t1.left = self.mergeTrees(t1.left,t2.left)
                t1.right = self.mergeTrees(t1.right,t2.right)

            elif t1 and t2:
                t1.val = t1.val + t2.val
                t1.left = self.mergeTrees(t1.left,t2.left)
                t1.right = self.mergeTrees(t1.right,t2.right)
                
        return t1