It's the mania basically. BP1 will include mania, by itself or in mixed states. BP2 has hypomania, tends to have more depression (but that varies).

Technically, one episode of mania classifies you as BP1. Technically, that is my diagnosis because I have had very rare episodes of mania and more commonly mixed states, but honestly, I spend much more time in depression and am probably more on the spectrum towards BP2. That's the thing about bipolar disorder; it really is on a spectrum and everyone presents a bit differently. So, in the end, the treatment for a person's specific presentation is what is most important. It is definitely not a one-size-fits-all diagnosis.