如何打印函数中的变量？（python）

class trie_node:
    def __init__(self):
        self.children1 = dict()  
        self.valid = False

class Trie:
    def __init__(self):
        self.root = trie_node()

    def insert(self, word: str) -> None:
        node = self.root
        for l in word:
            # print(l)
            if l not in node.children1:
                node.children1[l] = trie_node()
                node = node.children1[l]  # This is what I want to print out!! the value of children1.....
                # print(node.children1[l])
                node.valid = True

obj = Trie()
print(obj.insert('apple'))

如上，我想打印node的值，其实应该是一个一个字母的。。但是。。。

Traceback (most recent call last):
  File "2.py", line 40, in <module>
    print(obj.insert('apple'))
  File "2.py", line 18, in insert
    print(node.children1[l])
KeyError: 'a'

报错了。。不知道为什么，请教大佬指点！

程序不全