# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def isSymmetric(self, root):
        """
        :type root: TreeNode
        :rtype: bool
        """
        return isMirror(root, root)
        
        
def isMirror(t1, t2):
    if not t1 and not t2:
        return True 
    if not t1 or not t2:
        return False
        
    if t1.val == t2.val and isMirror(t1.left, t2.right) and isMirror(t2.left, t1.right):
        return True 
    else:
        return False