Rewrites a newick string so that the base is a trifurcation
        (usually means an unrooted tree)

def trifurcate_base(cls, newick):
        """ Rewrites a newick string so that the base is a trifurcation
        (usually means an unrooted tree) """
        t = cls(newick)
        t._tree.deroot()
        return t.newick