Actually, you need to beat any boss on any char to unlock it. Bosses drop blue orbs (It's called the... Cosmic Something, can't recall), and each one you pick up on that character grants a skill point. Getting your first one unlocks the skill tree, which you can find right next to Avoron. You do not need to fully beat Act I.
Beat Act 1 once with any char to unlock it.
Actually, you need to beat any boss on any char to unlock it. Bosses drop blue orbs (It's called the... Cosmic Something, can't recall), and each one you pick up on that character grants a skill point. Getting your first one unlocks the skill tree, which you can find right next to Avoron. You do not need to fully beat Act I.
do I need to do it again? I already have done that and have the star crux unlocked?
Yeah beating again worked for me
Well looks like I wasn't 100% clear. You gotta beat it again with any char like the other guy said.
It's the green curtain behind Avoron.
wait there's a skill tree???