如何打印使用类实现的树形数据结构？

class TreeNode:
    def __init__(self, value):
        self.value = value
        self.children = []

    def add_child(self, child):
        self.children.append(child)

   A
  / \
 B   C
    / \
   D   E

def print_tree(node, level=0):
    if node is None:
        return

    # 打印当前节点的值
    print(' ' * level + str(node.value))

    # 递归打印子节点
    for child in node.children:
        print_tree(child, level + 1)

root = TreeNode('A')
root.add_child(TreeNode('B'))
node_c = TreeNode('C')
node_c.add_child(TreeNode('D'))
node_c.add_child(TreeNode('E'))
root.add_child(node_c)

print_tree(root)

A
 B
 C
  D
  E