請實現一個函式，用來判斷一顆二叉樹是不是對稱的。注意，如果一個二叉樹同此二叉樹的映象是同樣的，定義其為對稱的。

class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None
class Solution:
    def sysmmetrical(self, root1, root2):
        if root1 == None and root2 == None:
            return True
        if
 
 root1 == None or root2 == None:
            return False
        if root1.val == root2.val:
            return self.sysmmetrical(root1.left, root2.right) and self.sysmmetrical(root1.right, root2.left)
    def isSymmetrical(self, pRoot):
        # write code here
        return self.sysmmetrical(pRoot,
 
 pRoot)