Multiboot installation on Raspberry Pi

Hello,

I am pretty new to Alpine Linux and Raspberry Pi as well. Anyway, i did a lot to search to find a way to install Alpine Linux on Raspberry using a multiboot, to have the choice on booting on Alpine and say Raspian (or any other distro), but i can't find any response.
I did not find any way to install alpine with berryboot for instance because i need a .img file to convert it to SquashFS, although the raspberry alpine file is tar.gz :(

Does anybody know to do, with berryboot or with any other multi-bootloader ?

Any help would be very nice

Thanks