Thanks a lot! The tree should light up after you connect the tree board and it must have at one point since you got to the next part, which is the screen flickering (technically "there's an issue with the world's nEon supply").
I'm glad to hear about your comment on that, I wasn't aware that it could get to the point where it's annoying to the eyes.
The solution is to enter the Hub Control building and push the button in the center there. That was put in there due to time constraints, since actually a boss battle was planned there. But I ran a bit short on time to add all that...