Level 10 is currently the maximum level.
After that point level 10 is just replayed over and over again.
(at least in the itch.io version)
In the current version there are many levels.
I plan into adding up to 25 levels with a boss at every 5 levels.
After you defeat the base difficulty you will unlock NG+, NG+2, etc.
The game and the beta will also be available on mac, if everything goes as planned.