Walnut is an option. I am not going for oak as I already have a couple.

So far, the options a
- Orange/clementine tree
- Mango (will need protection for the first few years) Not a favourite as it is not native.
- Wallnut
- Almond (Although I think roots are quite bad for the well)
- Chestnut

I kind of like the idea of some sort of nut tree.

Thanks