fixed for me thanks alot
Hi Hans.
Could you please give a quick rundown on what propulsion setup you are using? I’m not sure if the crash was an aircraft failure. You might have just been a bit unlucky with the tree. 
Looks like a nice QP build though!
forward propulsioN is important
Nice running gear! 
You say you flew it a few times. Did it yaw on every transition or just the one time?
I can only advise to try it again once you have rebuilt. Angling the hover motors forward might give it a bit more stability from the wings, but I can’t tell if hitting the tree caused the crash, or it “crashing” caused it to hit the tree! There are some vibrations, did a motor/prop come loose maybe? Also without running prop calc on your config, are the 12x8 a good match for the hover prop motors? Seems maybe the pitch is a bit high?
When you do your transitions maybe use qhover to stop rather than qloiter, this will not stop so abruptly by pitching up, and allow the transition to be a lot smoother. Qloiter is trying to position hold but Qhover will only hold altitude. Just make sure you have enough space to stop. BTW whilst getting used to quadplane performance etc I recommend using a bit more altitude when testing and tuning. The air is soft the ground and trees are not! 
It was yawing every time to the left. Maybe the front motor angle was not correct.
haha conclusion → cut the tree down…
There are some vibrations, did a motor/prop come loose maybe?
no motor/booms were fine after the crash