如何实现基于字符串对象键的面向对象的二叉树

class Node:
    def __init__(self, key):
        self.key = key
        self.left = None
        self.right = None

def create_binary_tree(keys):
    root = None
    for key in keys:
        root = insert_node(root, key)
    return root

def insert_node(root, key):
    if root is None:
        return Node(key)
    if key < root.key:
        root.left = insert_node(root.left, key)
    else:
        root.right = insert_node(root.right, key)
    return root

def search_node(root, key):
    if root is None or root.key == key:
        return root
    if key < root.key:
        return search_node(root.left, key)
    return search_node(root.right, key)

def preorder_traversal(root):
    if root:
        print(root.key)
        preorder_traversal(root.left)
        preorder_traversal(root.right)

def inorder_traversal(root):
    if root:
        inorder_traversal(root.left)
        print(root.key)
        inorder_traversal(root.right)

def postorder_traversal(root):
    if root:
        postorder_traversal(root.left)
        postorder_traversal(root.right)
        print(root.key)

def delete_node(root, key):
    if root is None:
        return root
    if key < root.key:
        root.left = delete_node(root.left, key)
    elif key > root.key:
        root.right = delete_node(root.right, key)
    else:
        if root.left is None:
            return root.right
        elif root.right is None:
            return root.left
        root.key = get_min_key(root.right)
        root.right = delete_node(root.right, root.key)
    return root

def get_min_key(root):
    while root.left:
        root = root.left
    return root.key