At first I thought ash, but the leaflets are a bit wide for that. I think its an elder. Anyway its a young tree so needs to come out!

I've got two of these come up in my garden, get it out quickly as they can grow into big trees, never found out the name of them, I'm still cutting mine down as I can't get mine out, think I may have to drill holes in mine & use stump killer.

Yep, probably an Elder. "Gift" of a bird. :)

Looks like Ash to me.

Well, that is possible. A good close-up of where the leaves join the stem would settle the matter--Elder leaf bases join together around the stem, while Ash leaf bases don't.

Just had a thought - bruise a leaf firmly between finger and thumb and sniff your finger. Elder smells strongly, Ash doesn't.