Till recent I was sure there could be no Folders in the Model Browser structure of Part-model (because I don't know how to create it manually).
I was surprised to know the BrowserPane.AddBrowserFolder Method in fact is not limited to Assemblies.
Below is the iLogic code that creates the custom object (WorkPlane), Folder, and puts the object into the folder:
Dim oDoc As Document = ThisApplication.ActiveDocument
Dim cmpDef = oDoc.ComponentDefinition
Dim oPane As BrowserPane = oDoc.BrowserPanes.ActivePane
Dim oTOs As TransientObjects = ThisApplication.TransientObjects
Dim subNodes As ObjectCollection = oTOs.CreateObjectCollection
Dim oWPl As WorkPlane = cmpDef.WorkPlanes.AddByPlaneAndOffset(cmpDef.WorkPlanes(1), 0)
Dim node = oPane.GetBrowserNodeFromObject(oWPl)
subNodes.Add(node)
Dim oFolder As BrowserFolder = oPane.AddBrowserFolder(, subNodes)
Here is a result if after run within the new IPT:

The folder can be expanded and collapsed, It's child nodes can be deleted.
But there are some problems with doing other things that user expect to work:
- can't delete the folder itself (even empty).
- can't move nodes out and into the folder.
I'd like to know whether I'm missing something that can make the folder fully functional for Part?