I had the same question. Turns out, it's mostly a future possibility, and for most current use cases of branches in git, you would use a channel in pijul. At least that's how I understand these discussions in the pijul discourse.

https://discourse.pijul.org/t/phenomenological-pijul-or-piju...

https://discourse.pijul.org/t/working-without-channels/1047/...