Couldn't you just continue cutting down from the top? That seems like it would cut through without pinching the bar. Once it's free, it may come loose. Then again without seeing the whole scene, I can't judge that well. I just had a similar situation, but when the tree went up, it pinched the bar really good. By the time I got the saw out with the backup, I had minor damage to the saw and was done for the night. Next time I went out the wind had done the work for me, snapping the last little bit, thus knocking the pieces clear and pulling the top down. My plan for freeing the tree would have involved pushing or pulling with the tractor from a safe direction if not distance.