The HD baggers are notorious for shaking their head with a high speed wobble. That's why Laura Klock doesn't ride her HD bagger anymore. The problem originates in the rubber mounted swingarm/rear engine mount. The trees are a small part of the problem also. You can fix the biggest part of the problem by getting the poly rear engine/swingarm bushings. The engine stabilizer that mounts under the oil pan will help some but I personally don't think it's worth the price they get for them. That's what you can do with off the shelf parts. If you want more find someone with a frame jig and a welder...