The provided data-table does not have a ParentId column, so the TreeView can be bound only with first-level nodes in a similar way:
If you want to group the data (e.g. by department code or name) you will need to aggregate your data and add an "ParentID" column that will hold the data determining the hierarchy of the nodes. You can find detailed information about the specifics on binding RadTreeView to a database here:
The following demo also represents a very simple demo for such setup so I will advise you to review it:
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