code: def _concat_datetimetz(to_concat, name=None):
      
      # Right now, internals will pass a List[DatetimeArray] here
      # for reductions like quantile. I would like to disentangle
      # all this before we get here.
      sample = to_concat[0]
  
      if isinstance(sample, ABCIndexClass):
          return sample._concat_same_dtype(to_concat, name=name)
      elif isinstance(sample, ABCDatetimeArray):
          return sample._concat_same_type(to_concat)
docs: concat DatetimeIndex with the same tz
      all inputs must be DatetimeIndex
      it is used in DatetimeIndex.append also