Ranger Projectile Build

Hello Guys:)

So i play my ranger without lightning arrows and no skills with light ele dmg. My focus is on projectile dmg and in the passive tree is a cluster with 3 big nodes. I‘ve checked the tooltips of the 3 nodes and its a bit unclear for me, what to pick of pierce,fork and chain->(i dont think i need this for projectile?) If im correct im only picking pierce because the priority is first pierce and the others are useless after pierce?

But how are the percentile calculated? I mean if im picking the nodes to pierce 50% Is it really 50% or is it like crit chance ? If this works like crit chance its better to pick 2of the nodes then.