Make sure that your data set is fetched and fill the parameters as described bellow:

• Items: List of Id, ParentId (set as 0 if it is not a tree), Name and Order;
• BaseId: ParentId of the root level (0 for base level);
• ItemsSelectedList: Selected ids, spliced by commas;
• NumberOfPossibleSelections: 0 = Read only; 1 = Single select; >1 = Multiple select.