It is hard to be 100% certain without seeing one of the leaves flat-on to see the exact shape, but I am pretty sure that is one of the littleleaf lilac tribe. (It is for *sure* a lilac).
Also it is pretty common to see things like that, with a littleleaf lilac grafted onto another Syringa species' trunk (ideally, S. reticulata b/c it doesn't sucker much) to make a "tree form" thing. (Lilacs are naturally multistemmed shrubs).
I've never seen nor heard of a littleleaf-type lilac getting taller than 6-7' or so... it is possible they may slightly exceed that when grafted onto a trunk, just b/c of the trunk's own height (I do not know, have not SEEN any unusually tall specimens that way, but it seems not-impossible).
But I would absolutely not expect that grafted dealie to get more than 8-10' tall maximum, unless there is something I'm missing here and someone can actually point you to taller-growing examples of it.
(Frankly I'm not sure how tall you'd WANT a topgrafted tree-type-thing to get anyhow, as the graft points are usually not quite as sound as natural-grown branches)
Good luck, have fun,
Pat