code: def _check_if_ins_is_dup(self, start, insertion):
          
          is_dup = False    # assume no
          variant_start = None
  
          dup_candidate_start = start - len(insertion) - 1
          dup_candidate = self._ref_seq[dup_candidate_start:dup_candidate_start + len(insertion)]
          if insertion == dup_candidate:
              is_dup = True
              variant_start = dup_candidate_start + 1
  
          return is_dup, variant_start
docs: 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)