There is no proper way in the interactive interface of Mp3tag, but you may create an export script, which can count the folders, like this example script ...
1: $filename($getEnv('USERPROFILE')'\Desktop\Mp3tag.Export.txt',UTF-8)2: $loop($folderdepth(%_folderpath%))
3: 'Folderdepth: '$folderdepth(%_folderpath%)
4: $loop(%_directory%,1)
5: %_parent_directory%'|'%_directory%
6: $loopend()
7: 'Folder count: '%_max_counter%
8: $loopend()
9: 'Folderpath count: '%_max_counter%
DD.20150613.0947.CEST
You may check out the method there ...
/t/12767/1
DD.20150613.1033.CEST