<telerik:RadTreeView ID="RadTreeListUsers" runat="server" CheckBoxes="True" Width="585px" TriStateCheckBoxes="True" CheckChildNodes="True" meta:resourcekey="RadTreeListPermissionsResource1" />
var userValues = new HashSet<string>(users.Select(p => NodeValue.FormatTreeLabel(p.DataTypeName, p.ToDataTypeStateAutoId, p.ServiceAreaNum, p.OperationName, p.AttributeName)));
var userNodes = GetUserNodes(userValues);
RadTreeListUsers.Nodes.Clear();
RadTreeListUsers.Nodes.AddRange(UserNodes); //this line taking lot of time to load and display treeView