Hi John,
Greetings from Syncfusion support.
We have validated your requirement and understand that you want to drag and drop the selected node from TreeView to detail template Grid. We would like to inform you that we do not have support to achieve your requirement. But as a workaround we have achieved your requirement using JSInterop and OnNodeDragStop event of the TreeView.
In the OnNodeDragStop event, we have called JavaScript method in _Host.cshtml file to find the Id of the Grid when the record is dropped and sent the ID to server side to add the record. We have defined the value on GridColumn based on DraggedNode data.
Please find the sample demonstrating the solution from below link
In the shared sample we have just shown how to drop the dragged node from TreeView into Grid. You can customize the sample as per your requirement.
Note: Since it is a workaround, it has some limitations, ID property of DetailGrid must be specified uniquely and same to insert the record at particular Grid.
Please let us know, if you need any further assistance.
Regards,
Indhumathy L