code: def merge(self, items):
          
          if isinstance(items, BaseCollection):
              items = items.all()
  
          if not isinstance(items, list):
              raise ValueError('Unable to merge uncompatible types')
  
          self._items += items
  
          return self
docs: Merge the collection with the given items.
  
          :param items: The items to merge
          :type items: list or Collection
  
          :rtype: Collection