code: @UiThread
      public void notifyParentRemoved(int parentPosition) {
          int flatParentPosition = getFlatParentPosition(parentPosition);
          int sizeChanged = removeParentWrapper(flatParentPosition);
  
          notifyItemRangeRemoved(flatParentPosition, sizeChanged);
      }
docs: Notify any registered observers that the parents previously located at {@code parentPosition}
  has been removed from the data set. The parents previously located at and after
  {@code parentPosition} may now be found at {@code oldPosition - 1}.
  <p>
  This is a structural change event. Representations of other existing items in the
  data set are still considered up to date and will not be rebound, though their positions
  may be altered.
  
  @param parentPosition Position of the parent that has now been removed, relative
  to the list of parents only.