Is it the same thing that's been sprouting up in my back yard?
Probably not, but anyway illustrates some taxonomical features.
-- The base of each leaf is pretty symmetrical - so I reckon it isn't any kind of elm, which I think have a fairly reliable tendency for the base of the leaf to run a little lower on its stem on one side than the other.
-- Where the leaf stem (or petiole) attaches to the main stem, there's often some kind of leafy structure (stipule), here narrow curly things. That's a good clue, and here it seems to match up with Corylus avellana, common hazel.
Dang squirrels.
