Update README.md

Python/symmetric_tree.py

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+# Symmetric Tree
+
+class TreeNode:
+    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):
+        queue = [root.left, root.right]
+
+        while queue:
+            left_node = queue.pop(0)
+            right_node = queue.pop(0)
+
+            if not left_node and not right_node:
+                continue
+            if not left_node or not right_node:
+                return False
+            if left_node.val != right_node.val:
+                return False
+
+            queue.append(left_node.left)
+            queue.append(right_node.right)
+            queue.append(left_node.right)
+            queue.append(right_node.left)
+
+        return True
+
+root = TreeNode(1)
+root.left = TreeNode(2)
+root.right = TreeNode(2)
+root.left.left = TreeNode(3)
+root.left.right = TreeNode(4)
+root.right.left = TreeNode(4)
+root.right.right = TreeNode(3)
+
+solution = Solution()
+print(solution.isSymmetric(root))