Will get pictures up once back home.

A view showing the tree.

Looking at the fence, the light, the stinging nettles and the Bindweed would I be right in thinking you're in the UK? I'd honestly not worry about pruning the apple tree for a while. You have bigger fish to fry. The Bindweed, nettles and aforementioned brambles are more urgent.

This winter, when you've got the jungle more under control you can look into pruning apples on a UK website such as RHS. And by then it will be the right time of year. Next spring you might get some blossom and then you'll find out if your apple produces worthwhile fruit. When you do get around to it consider your goals. If you encourage 'head height' growth bear in mind that will mean the fruit will be above head height. Tricky to pick.

It looks as if the garden has been neglected for a good while given the size of that bird sown elder tree. You might also want to consider cutting that down before worrying about the apple. Elder is generally considered a weed species in a UK garden. Yours is currently loaded with berries so a bit of jelly or wine making might be fun before you take a saw to it.

This was a bramble patch that I cut down about a month ago and discovered the tree. It was full of fruit on one side but I removed it so energy could go into leaf and branch growth. The Elder will be coming out this Autumn/Winter.

Did you try an apple? Were they tasty?

They are sharp cooking apples Bramley Seedling. I have 12 x 2 year old cider apple trees coming in 2 or 3 months hence clearing land for an orchard. And a crash course in apple tree care!

These are the trees I have coming:-

Bittersweet varieties

Three Counties
Black Dabinett
Herefordshire Redstreak
Bloody Butcher

Sharp/Bittersharp varieties

Bramley Seedling (a second tree)
Stoke Red
Browns
Peasgood Nonsuch (because of the massive apples and weird name)

Sweet varieties

Katy
Court de Wick (high sugar = high alcohol content)
Northwood
Sweet Alford

If it's a Bramley it will be fine, I'm sure. They do tend to biennial bearing though. When you said it had fallen over and regrown I sort of guessed it might be a Bramley. If you're getting cider apples and this is going to be a working garden rather than purely decorative maybe the Elder would fit in with your home brewing ethos after all.

I discovered the tree under the brambles at the end of the garden (I used to have 70 chickens roaming in that area). There is also a pear tree peaking out of the brambles I have yet to cut back and what appears to be another apple tree and perhaps a cherry tree as well. The cleared area will be my new orchard for my long term cider making plans. I also have a very large plum tree but I will cut this down and re train the new growth to keep it at head height.

If you cut down the plum make sure you cut above the graft. And don't do it in Winter. Unlike other fruit trees stone fruit should be pruned in early spring or mid summer when the sap is rising. When dormant the are prone to Silverleaf. (note to US readers, this is UK specific advice)

Sounds like a potentially very interesting project.