More concurrently! I've learned -but am still smoothing out and completing memorizing- the prelude of Bachs first solo Cello suite (playing an octave below written pitch, natch).
In addition, I've started working on Invention number II in C minor -which is somewhat challenging... it wasn't written for electric bass (obviously) but the range falls in the capacity of a 6-string bass (if one plays it an octave lower than written pitch, again); however, there are a few parts when the high and low counterpoint parts are so far apart that I'll have to do some tapping, as they'll be two far apart for even my large hands to play in one position.
I know and can play the piece on keyboard... but it's interesting to transpose it to bass. At some point, I'll work out some or all of the Suite in E Minor that I play on classical guitar for bass too... but for now, I'm trying to work on some new pieces specifically for my new bass!