如何使用SQLAlchemy设置与关联对象的邻接列表？

from sqlalchemy import create_engine, Column, Integer, ForeignKey
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.ext.declarative import declarative_base

engine = create_engine('数据库连接字符串')
Session = sessionmaker(bind=engine)
session = Session()

Base = declarative_base()

class TreeNode(Base):
    __tablename__ = 'tree_node'
    id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey('tree_node.id'))
    children = relationship("TreeNode")

# 创建根节点
root = TreeNode()

# 创建子节点
child1 = TreeNode()
child2 = TreeNode()

# 设置父子关系
root.children.append(child1)
root.children.append(child2)

# 提交到数据库
session.add(root)
session.commit()

# 查询根节点及其所有子节点
tree = session.query(TreeNode).filter_by(parent_id=None).first()

# 打印根节点及其所有子节点
def print_tree(node, depth=0):
    print('  ' * depth + str(node.id))
    for child in node.children:
        print_tree(child, depth + 1)

print_tree(tree)