如何将字典转换为嵌套字典？

def convert_dict_to_nested_dict(dictionary):
    nested_dict = {}
    for key, value in dictionary.items():
        if isinstance(value, dict):
            nested_dict[key] = convert_dict_to_nested_dict(value)
        else:
            nested_dict[key] = value
    return nested_dict

dictionary = {
    'key1': 'value1',
    'key2': {
        'nested_key1': 'nested_value1',
        'nested_key2': 'nested_value2'
    },
    'key3': 'value3'
}

nested_dict = convert_dict_to_nested_dict(dictionary)
print(nested_dict)

{
    'key1': 'value1',
    'key2': {
        'nested_key1': 'nested_value1',
        'nested_key2': 'nested_value2'
    },
    'key3': 'value3'
}