Multiple Nested ScriptableObjects

I'm trying to create nested ScriptableObjects. So far I can add a child ScriptableObject to a parent object using AssetDatabase.AddObjectToAsset which is good. However, attempting to add a sub child object to the child adds the sub child to the parent instead. This is the code I'm using:

 public void CreateNestedStructure()
 {
     var parent = CreateInstance<ScriptableObject>();
     parent.name = "Parent";
     AssetDatabase.CreateAsset(parent, "Assets/Parent.asset");
      
     var child = CreateInstance<ScriptableObject>();
     child.name = "Child";
     AssetDatabase.AddObjectToAsset(child, parent);
      
     var subChild = CreateInstance<ScriptableObject>();
     subChild.name = "Sub Child";
     AssetDatabase.AddObjectToAsset(subChild, child);
      
     AssetDatabase.SaveAssets();
     AssetDatabase.Refresh();
 }

This is the result

I wish to have the Sub Child reside inside Child, to make the file structure more organized. I assume the problem is that Child is an object of the Parent asset and not an asset itself. Is it possible to achieve this structure somehow?