我有一棵简单的二叉树，我正在尝试查找树的最后一个节点

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

def find_last_node(root):
    if root is None:
        return None
    if root.left is None and root.right is None:
        return root
    last_node = find_last_node(root.right)
    if last_node is None:
        last_node = find_last_node(root.left)
    return last_node

# 创建一个简单的二叉树
#       1
#      / \
#     2   3
#    / \
#   4   5
root = TreeNode(1)
root.left = TreeNode(2)
root.right = TreeNode(3)
root.left.left = TreeNode(4)
root.left.right = TreeNode(5)

last_node = find_last_node(root)
if last_node is not None:
    print("最后一个节点的值为:", last_node.val)
else:
    print("二叉树为空")