docs: @UiThread
      private int getFlatParentPosition(int parentPosition) {
          int parentCount = 0;
          int listItemCount = mFlatItemList.size();
          for (int i = 0; i < listItemCount; i++) {
              if (mFlatItemList.get(i).isParent()) {
                  parentCount++;
  
                  if (parentCount > parentPosition) {
                      return i;
                  }
              }
          }
  
          return INVALID_FLAT_POSITION;
      }