docs: def make_ampal(self):
          """Generates an AMPAL object from the parse tree.
  
          Notes
          -----
          Will create an `Assembly` if there is a single state in the
          parese tree or an `AmpalContainer` if there is more than one.
          """
          data = self.pdb_parse_tree['data']
          if len(data) > 1:
              ac = AmpalContainer(id=self.id)
              for state, chains in sorted(data.items()):
                  if chains:
                      ac.append(self.proc_state(chains, self.id +
                                                '_state_{}'.format(state + 1)))
              return ac
          elif len(data) == 1:
              return self.proc_state(data[0], self.id)
          else:
              raise ValueError('Empty parse tree, check input PDB format.')