Python solution faster than 90% (Iterative) !!
```\nclass Solution(object):\n    def postorder(self, root):\n        s = []\n        li=[]\n        s.append(root)\n        if not root:\n            return\n 
```\nclass Solution(object):\n    def postorder(self, root):\n        s = []\n        li=[]\n        s.append(root)\n        if not root:\n            return\n        while(s):\n            temp = s.pop()\n            li.append(temp.val)\n            for i in temp.children:\n                s.append(i)\n        return li[::-1]
['Python', 'Python3']