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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def initial(key, **kwarg):
 """Create an empty dicttree. The root node has a special attribute "_rootname". Because root node is the only dictionary doesn't have key. So we assign the key as a special attribute. Usage:: {'_meta': {'_rootname': 'US'}} """

        d = dict()
        DictTree.setattr(d, _rootname = key, **kwarg)
        return d