I've been playing Payday: The Heist, which has three upgrade trees (assault, sharpshooter, support).
Each time you gain a level, you proceed one step further up one of the trees. You can only ever be on one tree at any one time, though you can change which tree you're on instantly at any moment.
Right now I've been upgrading each tree equally. However, I'm starting to wonder: is there enough XP in the game to allow me to fully upgrade every tree, or should I pick the one I like most and upgrade only that tree?