code: def model2subs2seqs(self) -> Dict[str, Dict[str, List[str]]]:
          model2subs2seqs = collections.defaultdict(
              lambda: collections.defaultdict(list))
          for model in self.find('sequences'):
              model_name = strip(model.tag)
              if model_name == 'node':
                  continue
              for group in model:
                  group_name = strip(group.tag)
                  for sequence in group:
                      seq_name = strip(sequence.tag)
                      model2subs2seqs[model_name][group_name].append(seq_name)
          return model2subs2seqs