docs: public int put(BaseRow sortKey, BaseRow value) {
  		currentTopNum += 1;
  		// update treeMap
  		Collection<BaseRow> collection = treeMap.get(sortKey);
  		if (collection == null) {
  			collection = valueSupplier.get();
  			treeMap.put(sortKey, collection);
  		}
  		collection.add(value);
  		return collection.size();
  	}