类中的Python二叉树属性问题

class TreeNode:
    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None

class BinaryTree:
    def __init__(self):
        self.root = None

    def insert(self, value):
        if self.root is None:
            self.root = TreeNode(value)
        else:
            self._insert(self.root, value)

    def _insert(self, node, value):
        if value < node.value:
            if node.left is None:
                node.left = TreeNode(value)
            else:
                self._insert(node.left, value)
        else:
            if node.right is None:
                node.right = TreeNode(value)
            else:
                self._insert(node.right, value)

    def search(self, value):
        return self._search(self.root, value)

    def _search(self, node, value):
        if node is None or node.value == value:
            return node
        elif value < node.value:
            return self._search(node.left, value)
        else:
            return self._search(node.right, value)

    # 其他操作方法...