But in 5.5 I think you can choose any of the t2's as long as you had a t1 already chosen. Like skill t2a lead to t3b but sometimes skill t2b didnt lead to t3b. The vanilla game was pretty straight forward when you looked at it's skill wheel (which isnt part of the game, you can google it though) it had arrows that pointed at where the skills lead. What I really wanted to know was how the choices get pulled. But be careful as you're only allowed 3 perks or abilities per skill so if you pick 2 t2's you'll never get a t3. I believe the way it works is that you need to choose a t2 ability before t3 choices are unlocked as a choice. So I'm still not 100% with out booting up the game.
I got bored and couldnt quite figure out to play against cheating AI. To be honest, soon after I posted this I quit playing the game.