为什么写：unorderable类型：int（）＆lt; NoneType（）？

Question

我得到了二进制搜索树的作业递归版本，我必须将数字从数组插入到BST，然后搜索它，查找数字是否存在（True）或不存在（False）。

class Node:
    def __init__(self, value, left, right):
        self.left = left
        self.right = right
        self.data = value

class BinarySearchTree:
    def __init__(self):
        self.root = Node(None, None, None)

    def insert(self, value):
        root = self.root
        new_node = Node(value, None, None)
        if root.data is None:
            root = new_node
        if new_node.data < root.data:
            if root.left is None:
                root.left = new_node
            else:
                root.left.insert(value)
                root = root.left
        else:
            if root.right is None:
                root.right = new_node
            else:
                root.right.insert(value)
                root = root.right

    def fromArray(self, array):
        for i in range(len(array)-1):
            value = array[i]
            BinarySearchTree.insert(self, value)
            i += 1
        return BinarySearchTree

    def search(self, value):
        if (self.root is not None):
            return self._search(value, self.root)
        else:
            return None

    def _search(self, value, node):
        new_node = Node(value, None, None)
        if (new_node.data == node.data):
            return True
        elif (new_node.data < node.data and node.left is not None):
            self._search(value, node.left)
        elif (new_node.data > node.data and node.right is not None):
            self._search(value, node.right)
        else:
            return False

    def min(self):
        root = self.root
        if root.left is None:
            return root
        else:
            self.min(root.left)

    def max(self):
        root = self.root
        if root.right is None:
            return root
        else:
            self.max(root.right)

即使我正在比较两个节点它写错误：

  

unorderable类型：int（）＆lt; NoneType（）

出了什么问题？