def _check_if_ins_is_dup(self, start, insertion):
is_dup = False    <EOL>variant_start = None<EOL>dup_candidate_start = start - len(insertion) - <NUM_LIT:1><EOL>dup_candidate = self._ref_seq[dup_candidate_start:dup_candidate_start + len(insertion)]<EOL>if insertion == dup_candidate:<EOL><INDENT>is_dup = True<EOL>variant_start = dup_candidate_start + <NUM_LIT:1><EOL><DEDENT>return is_dup, variant_start<EOL>
Helper to identify an insertion as a duplicate

        :param start: 1-based insertion start
        :type start: int
        :param insertion: sequence
        :type insertion: str
        :return (is duplicate, variant start)
        :rtype (bool, int)