I put the cemetery's name in Burial's "Place" field. I realize that this may horrify some people, but it works for me. I do not stick to the "4-levels of place" idea, because in my part of the world we have 3 levels of place, and in some parts of the world it is not uncommon to have 5 or even 6 levels of place.
Still, if you want to add a description to the Burial event, you should be able to use the instructions found when you search on "How to add a custom event or attribute". (The description would be an attribute.)