You could try using the Load-on-Demand functionality of the TreeList demonstrated in the example below:
Additionally, you could try using as you mentioned DetailTemplate or TreeListTemplateColumn with ItemTemplate and manually retrieve and show the needed information. Note that on update this will require saving the values in a ViewState and retrieving them so the TreeList is updated accordingly. This approach will help skip the TreeList rebind and improve the performance.
the Telerik team
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