Hi Alex,
there are a lot of examples in the community, may be therefore nobody wrote an answer.
You have to add the Full Path of the Folder to your query in Excel Report and sort by Path.
Here you can find help how to get the Full Path:
http://h30499.www3.hp.com/t5/Quality-Center-Support-and-News/How-to-find-the-find-the-path-of-folder-in-Test-Plan/td-p/4794578
kind regards,
A.E.