Hi nathaliev,
Looks like you need to rename the files with leading zeros in front of the single digits. Windows sorts them intuitively (now - it didn't used to), but apparently iTunes does not.
e.g.
Music Volume 2.1 - Track 01
Music Volume 2.1 - Track 02
Music Volume 2.1 - Track 03
Music Volume 2.1 - Track 04
et cetera