Drag Drop betwwen WPF DataGrid and WPF treeView

Question

I am making a WPF application , in which i have a datagrid which contains list of employees.

On the left of window i have a treeview which shows all departments & subdepartments.

What i want is that i select a employee / row in datagrid and drag it over to the specific node of treeview and finally i get the data of row/rows i selected so that i could move them to selected department. But i am unable to get logic on how to do drag n drop in WPF datagrid. Please help