def METHOD_NAME(self, ref, alt, alt_count, co_alt_count, skip=False):
    self.variants.METHOD_NAME(self.ParentVariant(ref, alt, alt_count, co_alt_count))
    if not skip and alt is not None and (alt_count, co_alt_count) in self.allowed_types:
        self.phasable.add(len(self.variants) - 1)
        self.nodes_modified = True