[SerializableAttribute()] 
public class GroupRelationCollection : System.Collections.ObjectModel.Collection<GroupRelation> 

class MyPage : System.Web.UI.Page
{
   private void SaveGroupRelations(Group grp)
   {
       // using additioal collection - to save sorting order
       // load group relations
       GroupRelationCollection relationsList = new GroupRelationCollection();
       for (int i = 0; i <= int.MaxValue; i++)
       {
           string pId = Request["GRPREL_ID" + i];
           if (string.IsNullOrEmpty(pId))
               break;

           GroupRelation g = new GroupRelation(grp.ID, pId);
           g.ID = grp.ID;
           g.ParentID = pId;

           relationsList.Add(g);
       }

       // remove all relations
       GroupRelation grpRelDel = new GroupRelation();
       grpRelDel.Delete(grp.ID);

       // save loaded relations
       foreach (GroupRelation g in relationsList)
       {
           g.Save(g.ID, g.ParentID);
       }
   }
}