docs: def tree_match(cls, field, string):
          ''' Given a tree index, retrieves the ids atached to the given prefix,
          think of if as a mechanism for pattern suscription, where two models
          attached to the `a`, `a:b` respectively are found by the `a:b` string,
          because both model's subscription key matches the string. '''
          if not string:
              return set()
  
          redis = cls.get_redis()
          prefix = '{}:tree_{}'.format(cls.cls_key(), field)
          pieces = string.split(':')
  
          ans =  redis.sunion(
              prefix + ':' + ':'.join(pieces[0:i+1])
              for i in range(len(pieces))
          )
  
          return sorted(map(
              lambda id: cls.get(id),
              map(
                  debyte_string,
                  ans
              )
          ), key=lambda x:x.id)