如何在中打印二叉树作为Python中的节点结构

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def print_tree(root):
    if not root:
        return
    
    print(root.val)  # 打印当前节点的值
    print_tree(root.left)  # 递归打印左子树
    print_tree(root.right)  # 递归打印右子树

# 创建一个二叉树
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)

# 打印二叉树节点结构
print_tree(root)