code: def is_insertion(self):
          
          # An insertion would appear in a VCF like C>CT, so that the
          # alternate allele starts with the reference nucleotides.
          # Since the nucleotide strings may be normalized in the constructor,
          # it's worth noting that the normalized form of this variant would be
          # ''>'T', so that 'T'.startswith('') still holds.
          return (len(self.ref) < len(self.alt)) and self.alt.startswith(self.ref)
docs: Does this variant represent the insertion of nucleotides into the
          reference genome?