Custom API 9.3 BaseTreeHierarchy

In the ApiSdk (https://github.com/OneIdentity/IdentityManager.ApiSdk/blob/v93/doc/02-entity-methods.md#hierarchy-configuration) there is documentation regarding BaseTreeHierarchy, which can set a new root when getting data from a foreign key. 

I can't seem to find this, is it not implemented or am I missing a reference?