sounds like a saw wave and sine together
played in lower octaves and has some of the top frequencies removed with a low pass filter.
When the longer notes play you can also hear that an ADSR envelope is set up to the the filter cutoff with the attack being at 0, decay being medium ish and the sustain level being lower than full so the tone changes when holding the notes for longer.
I actually find that Trilogy is great for bass sounds. In this case it sounds like a synth, however an alternative to getting this sound would be to distort an actually sampled bass from trilogy in Guitar rig or something and use that.
Just chucking in my tuppence because I’m more of a samples person