I would suggest you to check the FetchStrategy
class. It allows you to specify which navigation properties to be loaded along with the object that you query for. They can be defined either per query or per context.
In this set of documentation articles
you can find a variety of examples regarding the definition and the usage of fetch plans. Then you need to define the Hierarchy for the RadGridView and set the PropertyRelation as demonstrated in this help article
the Telerik team