如何打印基于对象层次结构的HTML标记？

class HTMLElement:
    def __init__(self, tag, attributes=None, children=None):
        self.tag = tag
        self.attributes = attributes or {}
        self.children = children or []

    def to_html(self):
        attributes_str = ' '.join([f'{key}="{value}"' for key, value in self.attributes.items()])
        children_str = ''.join([child.to_html() for child in self.children])
        return f'<{self.tag} {attributes_str}>{children_str}</{self.tag}>'

# 创建对象层次结构
html = HTMLElement('html')
head = HTMLElement('head')
title = HTMLElement('title', children=[HTMLElement('text', children=['Page Title'])])
body = HTMLElement('body')
h1 = HTMLElement('h1', children=[HTMLElement('text', children=['Hello, World!'])])

# 构建对象层次结构
html.children = [head, body]
head.children = [title]
body.children = [h1]

# 打印HTML标记
print(html.to_html())