I'm playing with your TechTree right now and it is pretty good. But I guess i've found a little bug
The 1.875 Protective Shell is placed under Advanced Construction. But all the others are can be unlocked with the aerodynamic nodes. So I guess this one should go under the Advanced Aerodynamics
And is there a specific reason, why we're getting all the 1.875 parts before 2.5m (which makes sense), but all the engines for this tierr are above 2.5m?