code: def expand_dims(self, axis):
          
          if axis == -1:
              axis = self.ndim
          array = np.expand_dims(self, axis)
          if axis == 0:
              # prepended an axis: no longer a Timeseries
              return array
          else:
              new_labels = self.labels.insert(axis, None)
              return Timeseries(array, self.tspan, new_labels)
docs: Insert a new axis, at a given position in the array shape
          Args:
            axis (int): Position (amongst axes) where new axis is to be inserted.