Indent / Foldout for sub-sub-assets in Project View?

If I create an asset and add a subasset to it using AssetDatabase:

Code (CSharp):

1. // within the MainAsset context
2. AssetDatabase.AddObjectToAsset(mySubAsset)

Then the MainAsset will then have a foldout and I can see mySubAsset within the Project View.

Now if I add another object to mySubAsset

Code (CSharp):

1. // within the mySubAsset context
2. AssetDatabase.AddObjectToAsset(mySubSubAsset)

Then I will see both mySubAsset and mySubSubAsset within the MainAsset foldout within the Project View. They are essentially displayed like they are siblings in this structure.

Is there a way to further indent these? Or to have foldouts for sub-assets so that we can nest assets in a tree like structure? I would like to be able to have the parent/child relationship of multiple sub-assets within one asset file. Is a view like this possible in the Project View?

I know that I could use TreeView and make a custom editor window, just wondering if there is a workaround

Thanks