code: public void insertGroup(int inserted, @Nullable List<L> groups) {
          if (inserted < 0 || inserted >= mCards.size() || groups == null || groups.size() == 0)
              return;
  
          List<L> cards = getGroups();
  
          boolean changed = cards.addAll(inserted, groups);
  
          if (changed)
              setData(cards);
      }
docs: insert groups after position inserted
  
  @param inserted index that will inserted after
  @param groups   new groups