Besides the trivial tabular data visualization, the RadGridView is capable of displaying hierarchical data in the form of nested tables. In this case the rows of the RadGridView are represented by the GridViewExpandableRow class. In the Basic Hierarchies topic you can find information about the basics of building a hierarchical grid.
The RadGridView also allows you to create hierarchies in your grid based on some custom logic. In that case you can benefit from the RowDetails options. To learn more about these take a look at the Row Details topic.
In the cases when the nested grids should display data of the same type as the master grid, you can build a self-referencing grid. To learn more about the self-referencing approach take a look at the Self-Referencing GridView topic.
Please bear in mind that the DataContext of the row details presenter and the hierarchy child presenter is the parent row and not the context of the RadGridView itself. You can change the DataContext either in the LoadingRowDetails event when dealing with row details or in the DataLoding event when building a hierarchy with table definitions.