Indeed, so a skill tree would then branch such that the two are separate.
I cannot believe you people have this much difficulty grasping how even though the function is correct, the perk tree is visually broken; no matter what you say about it -> because it implies progression where said progression is actually impossible.
It does branch. Its just both branches arrive at the same place.
Logic dictates that the advanced skills of a particular branch can only be arrived at if you have learned the lesser skills first.
Could they have designed it better? Maybe, but then that would mean identical perks at the end of each branch, or seperate perks for Dragonbone and Dragonplate armour. Personally, I would have gone with the latter. I dont think its worth getting overly annoyed about though.