I think that you very significantly underestimate the resistance value of even modest trees: Even modest trees weight a lot. Carry some larger wood trunk pieces to get a feeling for it. Now imagine that piece of wood being thrown at you with 100 km/h and tell me again it is no issue. Trees tend to be rooted.... so the trunk wont give in much or even at all. You will not fell it... you will chop it off.... by overcoming the entirety of the woods structural integrity. That is a lot of stopping power.... At the speeds car tend to move, the tree has literally no time to bend in..... instead this resistance will be added to the severity of the impact. Cars tend to hit trees near the ground.... your leverage is at the minimum while the roots grant maximum resistance there. Trees by all means and accounts counts as a pale impact. This means maximum penetration power as all of the force is concentrated in a small area. In english.... hitting anything like an even small but proper tree will most likely cause very significant damage to your car and most likely even yourself. Even if you manage to chop it off, the upper part of the tree is now free floating... aiming cleanly at your windshield which will certainly not stop such an impact. That is not to say that you cant chop of a tree with a car..... after all the destructive potential of at least a metric ton of metal moving at speed is widely underestimated. I am just saying that you will most likely not fondly remember it, assuming you survive.