Another passed Java solution
public class Solution {\n        public boolean isSymmetric(TreeNode root) {\n            if (root == null) \n                return true;\n            \n      
    public class Solution {\n        public boolean isSymmetric(TreeNode root) {\n            if (root == null) \n                return true;\n            \n            return isSymmetric(root.left, root.right);\n        }\n        \n        boolean isSymmetric(TreeNode left, TreeNode right) {\n            if (left == null && right == null) \n                return true;\n\n            if (left == null || right == null) \n                return false;\n\n            if (left.val != right.val) \n                return false;\n\n            return isSymmetric(left.left, right.right) && isSymmetric(left.right, right.left);\n        }\n    }
['Java']