About 6 months ago I sat down to tackle writing a custom skill tree system in Unity. I wanted a visual editor that could easily assemble a tree at the same complexity level of Skyrim. And magically assemble all the data into a visual output without lifting an extra finger. After a couple days of combining some old scripts with a shiny new interface I created Unity Skill Tree Pro. A free plugin that makes complex skill tree management automated.
This is just the first iteration of Unity Skill Tree Pro. So the visual editor is still a little rough. That said it does a lot out of the box right now. If you want to customize it further the source is freely available online and it was written to be easily extendable without touching source code.