'Print trace output displaying the fringe of ``tree``.  The
fringe of ``tree`` consists of all of its leaves and all of
its childless subtrees.
:rtype: None'

def _trace_fringe(self, tree, treeloc=None):

    if (treeloc == ()):
        print(u'*', end=u'    ')
    if isinstance(tree, Tree):
        if (len(tree) == 0):
            print(unicode_repr(Nonterminal(tree.label())), end=u'    ')
        for i in range(len(tree)):
            if ((treeloc is not None) and (i == treeloc[0])):
                self._trace_fringe(tree[i], treeloc[1:])
            else:
                self._trace_fringe(tree[i])
    else:
        print(unicode_repr(tree), end=u'    ')
