When I prune my apples and pears in spring, I keep some of the pruned branches to dry for the grill but use some of the branches as supports and border fencing in the garden, and stick some of the branches in the surrounding ground.
The ones stuck in the ground sometimes leaf out and bloom, but usually does not strike roots and are dead by the time they need to be cleaned up for re-planting the bed or by Fall.
Also, there are usually some volunteer seedlings that grow from most probably bird-sown seeds. I let some of those grow just for fun. But most of the apple-like seedlings are from the crabapple tree with tiny yellow pea-sized fruits which was itself a volunteer way back when.
In my Espalier Fence Row, one of my trees died a couple of years ago when it was girdled by rodents or rabbits over the winter. I haven't cut down/dug up the dead tree yet but I really need to replace it and have been shopping for what to plant in its place -- OK to plant another apple? Should it be some other fruit?
...but I noticed this spring that there is what looks like an apple growing halfway between the dead one and the Seckel pear, the next tree over. I left it to see if it would survive -- sometimes the volunteers are from store bought apple seeds and they exhibit common local diseases that would kill them or at least affect them severely (there's one in the Kid's Garden that gets covered by Downey mildew every year -- very slow to grow -- that I'm still trying to decide whether to keep though it's been about 4 years)
This volunteer in the Espalier row got a bit of fireblight, but seems to have shrugged it off.
Since I don't tag the prunings I stick in the ground, I have no idea if this is one (though I vaguely remember sticking one around there before) or if it might be a volunteer seedling. It could even be from a dropped fruit from the lost Pristine.... And another possibility is that it's a root sucker from the Pristine's rootstock.