Apple Tree losing bark

Looks like physical damage to the young bark originally, possibly caused by animals or kids or an old stake, which has now spread.

I wouldn't give up on the tree yet. When the leaves have fallen prune out a couple of the larger branches from the center to open it up and to give the roots less top to provide for. Where you currently have some plastic wrapped round the trunk take that off, and clean up any dead branches flush to the trunk with a saw or a sharp knife. Re-bandage the trunk with plastic sheeting wrapped round it from below the damage to above it - get it fairly tight and secure with sticky tape or string. Leave this bandage on until the middle of next summer then unwrap it and see how things look then.

I had some fairly extensive deer damage to the bark on several of my apple trees a few winters ago almost ringing the trunks, but I have managed to bandage up the trees as described, and they are growing again OK now.