We use the TreeList control in our ASP .NET 4, C# application (running on Internet Explorer). 
In a page we have a Repeater of Update Panels. Each Update Panel contains a TreeList. All TreeLists have the same behaviour. They have multiple sorting enabled, and by default they are sorted by 2 columns (Class, ID). When sorting by some other column (Example: State), we adjust the Sorting Expressions from (Class, ID, State) to (State, ID). The sorting icon is not visible on the State column, but we have a simple button with no text on the Class column.