Python - Update dict in a cascade manner

def update_dict_cascade(dict_1, dict_2):
    """
    Update dict_1 with dict_2 in a cascade manner.
    :param dict_1: The dict to be updated.
    :param dict_2: The dict used for updating.
    :return: The updated dict_1.
    """

    if dict_1 == dict_2:
        pass
    else:
        for k, v in dict_2.items():
            try:
                v1 = dict_1[k]
                if not isinstance(v1, dict) or not isinstance(v, dict):
                    dict_1[k] = [v1, v]
                else:
                    dict_1[k] = update_dict_cascade(v1, v)
            except KeyError:
                dict_1[k] = v

    return dict_1

Test:

a = {'a': {'aa': {'aaa': 1}}}
b = {'a': {'aa': {'bbb': 2}}}
c = {'a': {'bb': {'ccc': 3}}}
d = {'b': {'bb': {'ddd': 4}}}
e = {'c': {'cc': {'eee': 5}}}


print(a)
update_dict_cascade(a, b)
print(a)
update_dict_cascade(a, c)
print(a)
update_dict_cascade(a, d)
print(a)
update_dict_cascade(a, e)
print(a)


Output:
{'a': {'aa': {'aaa': 1}}}
{'a': {'aa': {'aaa': 1, 'bbb': 2}}}
{'a': {'aa': {'aaa': 1, 'bbb': 2}, 'bb': {'ccc': 3}}}
{'a': {'aa': {'aaa': 1, 'bbb': 2}, 'bb': {'ccc': 3}}, 'b': {'bb': {'ddd': 4}}}
{'a': {'aa': {'aaa': 1, 'bbb': 2}, 'bb': {'ccc': 3}}, 'b': {'bb': {'ddd': 4}}, 'c': {'cc': {'eee': 5}}}