Opera video

Hi,
I have several opera recordings divided in acts. So, my opera videos folder look like

Opera videos
-> Walkure
-> -> Act 1
-> -> -> Act 1.mkv
-> -> Act 2
-> -> -> Act 2.mkv
… etc

Beside merging video files in one huge Walkure.mkv, are there any naming conventions how to see them in Kodi menu under Opera videos -> Walkure.
I can make custom menu for “Opera videos” (http://kodi.wiki/view/custom%20home%20items), but not know how to rename acts. Pattern Wagner – Act 1.mkv is not very elegant.
Any help, please