What kind of tree is this?

Went out for a walk when The Boy finished school today. I took a few photos and a couple were suitable to be blips which is going to annoy me when I have a day without a blip - probably tomorrow.

Anyway, I was trying some macro-like shots - it's something I have to for a dodgy-magazine-photography-course-thing and to be honest, my heart's not in it at all but looking through the photos after the walk, I really liked this one. So here it is, rather than the one I took specifically to be blip'd. I reckon I can do the other one when I'm struggling another day - I think this is what my colleagues are calling "a blip in the can".

There's no prize for the first person to tell me what kind of tree this is.