I will always remember the huge old apple tree that grew behind my parent's property in Indiana, on the southern hedgerow bordering a field usually planted to soybeans and occasionally corn. The tree was clearly feral, as you say, and huge, the forked trunk was at least a foot and a half across. The apples were small, but edible when properly ripe. It never seemed to have been part of an orchard, so it likely came from a random pip.
As children, that tree was the focal point for a lot of our neighborhood childhood play. We climbed it, made forts under it's shade, ate the apples (green or ripe), used the rotten, vinegary apples as ammunition in pretend war games. Every neighborhood child knew that tree, and if you said "meet me at the apple tree after lunch", they knew exactly where that was! My mother would even humor us and make an apple pie from the apples (when ripe of course). When we were a little older, that came with "...if you help peel, core, and cut them up". Most of the apples were no more than a couple inches across, ripened yellowish, with the occasional red streak.
I was sad when the old tree died, long after my childhood. I still have a short cylinder of wood cut from one of the dead branches, I use it as a paperweight sometimes, but mostly it is just something to remember the tree by.