docs: @UiThread
      public void notifyParentInserted(int parentPosition) {
          P parent = mParentList.get(parentPosition);
  
          int flatParentPosition;
          if (parentPosition < mParentList.size() - 1) {
              flatParentPosition = getFlatParentPosition(parentPosition);
          } else {
              flatParentPosition = mFlatItemList.size();
          }
  
          int sizeChanged = addParentWrapper(flatParentPosition, parent);
          notifyItemRangeInserted(flatParentPosition, sizeChanged);
      }