Entity collection hierarchy

When working with PrimitiveCollections I could add collection to a collection.
More specifically, I have 3 types of data to show on the map and I once used the primitive collections to seperate them. So far, when trying to add an EntityCollection to an EntityCollection I get the “child collection” converted into an entity…
Can we create hierarchy as in the primitive collection? If not, is there a way to seperate groups of entities while still working with the viewer’s entities?

I’ll reply here myself if anyone missed that in the tutorial (couldn’t find it there though…).
Entities can be divided into dataSources, using the CustomDataSource.