Dispatch a tree build call. Note that you need at least four
        taxa to express some evolutionary history on an unrooted tree.

def build_tree(self, *args, **kwargs):
        """Dispatch a tree build call. Note that you need at least four
        taxa to express some evolutionary history on an unrooted tree."""
        # Check length #
        assert len(self) > 3
        # Default option #
        algorithm = kwargs.pop(kwargs, None)
        if algorithm is None: algorithm = 'raxml'
        # Dispatch #
        if algorithm is 'raxml':    return self.build_tree_raxml(*args, **kwargs)
        if algorithm is 'fasttree': return self.build_tree_fast(*args, **kwargs)