So, about this skill-tree I've been thinking of setting up,
As opposed to edges, I'm thinking of using straight-up stunts that characters can do. Players who go up magic trees will earn new base spells, melee and ranged characters will earn new combat maneuvers, and the maneuvers and spells would have prerequisite levels and/or other maneuvers and spells.
So, for example, the Dark Magic path has "Hack Undead" as one of the low-level abilities, which allows you to control pre-ressurrected undead creatures, which you will need in order to unlock "Raise undead" which allows you to raise your own zombies.
Classes start out with stunts/spells/maneuvers/whatever you want to call them in the middle of various branches, and have an advantage in the fact that they don't need prerequisites in order to learn skills further down the branches, and can upgrade quicker down the tree, learning things up their alley faster than other classes.
So, for example, where a one class that wasn't involved in that particular tree would need to go through all the motions of learning the prerequisites in order to get to a certain skill, another would already have that certain skill, and would then proceed to learn the prerequisites to that skill to easily learn other skills.
The problem is, I can't think of that many ranged and melee stunts, or how to effectively, but not overpoweredly introduce a "Backstab" stunt for the Assassin class.