It's a Prunus of some sort, which includes both fruiting and flowering cherries, plums and apricots. Without seeing the entire tree and in leaf, I'd guess it to be some sort of ornamental cherry.

Was it blooming recently? The incredibly mild, warm fall and winter much of the NE is experiencing has resulted in a lot of out of season flowering of ornamental cherries.

Thank you for your response! I am in the NE, and it was blooming recently, though only half of the flowers were in bloom. I'm guessing it is the cherry...

I think it is Prunus subhirtella 'Autumnalis rosea'. You say you are in the NE - but not which country. If NE England then that's what it is.