code: def add_dataset(self, task_name, dataset=None, *, aliases=None):
          
          self._datasets.append(dataset if dataset is not None else TaskData())
          last_index = len(self._datasets) - 1
          self._aliases[task_name] = last_index
  
          if aliases is not None:
              for alias in aliases:
                  self._aliases[alias] = last_index
  
          if len(self._datasets) == 1:
              self._default_index = 0
docs: Add a new dataset to the MultiTaskData.
  
          Args:
              task_name (str): The name of the task from which the dataset was received.
              dataset (TaskData): The dataset that should be added.
              aliases (list): A list of aliases that should be registered with the dataset.