如何在嵌套字典中合并具有相同键的值？(不起作用)

def merge_dicts(dict1, dict2):
    for key in dict2:
        if key in dict1 and isinstance(dict1[key], dict) and isinstance(dict2[key], dict):
            merge_dicts(dict1[key], dict2[key])
        else:
            dict1[key] = dict2[key]

dict1 = {
    'a': 1,
    'b': {
        'c': 2,
        'd': 3
    }
}

dict2 = {
    'b': {
        'c': 4,
        'e': 5
    },
    'f': 6
}

merge_dicts(dict1, dict2)
print(dict1)

{
    'a': 1,
    'b': {
        'c': 4,
        'd': 3,
        'e': 5
    },
    'f': 6
}