David Linden

If you look at the second picture from the top, down along the stem it appears that the leaves are alternate in arrangement.  The picture is poor, so I could be mistaken. The leaves at the tip of the twig seem to be opposite, but there is some discrepancy between the two. The leaflets don't count, only the compound leaves as a whole.

The compound leaf is the easiest character to rule out pawpaw.  The leaf does resemble ash, but it appears to have alternate branching (not the leaflets, but the whole compound leaf) which rules out ash. Don't know what it is, but not pawpaw or ash.