Parent/Child Folder Entity (self loop) - how to list root folders (with no parent) with XPath

Hi all,

I have a Folder entity that has an association to itself (in a database table, I would have a ParentFolderId property pointing to the FolderId property in the table). I want to list all the root folders (with ParentFolderId = null), but I can't seem to be able to do this with XPath. If I do not(Association), it shows me only the folders with no association. But if a root folder has a child, then it has an association and it doesn't show. I'm assuming there's an easy way to do this and I am just not seeing it.

Many thanks

Gonçalo