If you are level 10 Strength, for instance, that means you have access to at least the first level in ALL TEN perks under Strength. You have to look not just across, but up and down. I’ve seen players start maxing out specific SPECIAL attribute letters early, or even trying to max out ALL of them, because they don’t understand how the system works.
Though I really like the functionality of the skill tree, knowing how to use it can be tough. The Answer: Again, this is poorly explained in the game, and has the potential to derail your entire playthrough if you’re not careful. The Question: “Okay I’ve started maxing out the letters, when do I get perks?”