Any more pics showing the foliage better? Looks most like a hawthorn Crataegus of some sort, but not one of the common ones. Also superficially like a Whitebeam Sorbus aria, but the white lower surface of the leaves conspicuous in that isn't present here.
That was the best photo of the leaves.They are oval shaped and serrated. They aren't lobed shaped or white underneath. The flowers grow in clumps. The stamens are very long. It was the first thing I noticed. Below is the college it was near. I think it was Trinity college. The ivy on the front of the building is a virginia creeper or Boston ivy. The photos were taken in mid- May. Hope that helps.
