There is no specific requirement for the stucture of the data you want to use in the TreeListView control. However, you are responsible for building the proper hierarchy that will make the data suitable for usage in the UI of your application. In most business scenarios it is not feasible to change the structure of your databases just for the sake of UI and it is usually better and easier to process the data in the ViewModel of your application to make it suitable for rendering (if you are using a design pattern like MVVM).
I am pasting below a link to a blog post that demonstrates how to use a converter to build a hierarchy from a originally flat collection of data. You may find that approach useful.
the Telerik team