code: def initial(key, **kwarg):
          
          d = dict()
          DictTree.setattr(d, _rootname = key, **kwarg)
          return d
docs: 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::
  
              >>> from weatherlab.lib.dtypes.dicttree import DictTree as DT
              >>> d = DT.initial("US)
              >>> d
              {'_meta': {'_rootname': 'US'}}