Header nodes in a treeview bound to a dataset

Hello!

I've relational data in a dataset that should be displayed in a treeview hierarchically (e.g.  datatables "customer", "orders", "shipping notes" and "invoices" with parent-child relationships between"customer" - "orders", "orders" - "shipping notes" and "orders" - "invoices").

I used a hierachical data template that worked fine but I need to have something that I would call "header nodes". The bound treeview should look like this:

Customer 1

    Orders (<- Header node)

        Order 1

            Shipping Notes (<- Header node)

                Shipping Note 1

                Shipping Note 2

            Invoices (<- Header node)

                Invoice 1

        Order 2

        Order 3

Because the dataset structure corresponds to the database structure I'm not able to change the data model to archieve this.

What does the trick?

Thanks for your help!