您必须检查递归调用是否确实找到了某些东西，以便您可以继续循环。例如。尝试以下操作：

You have to check whether the recursive call actually found something so you can continue the loop. E.g. try the following:

def tree_traverse(tree, key):
    for k, v  in tree.items():
        if k == key:
            return v
        elif isinstance(v, dict):
            found = tree_traverse(v, key) 
            if found is not None:  # check if recursive call found it
                return found