Can you please refer to answer from 29-Dec-2014
in ticket with ID: 876775
, where I have explained in details how you could achieve such behavior:
"Since your HierarchyLoadMode is set to ServerOnDemand, once you expand an item you can get reference to the NestedViewTemplate withing the server-side OnItemCommand event handler and depending on your enumeration, to select a specific RadTab in the RadTabStrip control..."
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