Prunus padus, aka Bird Cherry, is what that would be here. Prunus serotina has similar flowers but I don't know it well enough to id. Both produce fruit but they are not much use for human eating.

floral_uk,

Thank you for identifying it as Prunus padus. After comparing the pictures on the net, definitely it is padus rather than serotina. I will have to tell everybody not to eat the fruits. But the tree is so pretty this time of the year!

The fruit isn't poisonous but I doubt anyone would try more than a couple. They are small and sour but have been used as food in some places at some times.

Here is a link that might be useful: Bird cherry fruit

The one that looks like Prunus padus is P. virginiana.

bboy - I'm glad you chipped in because I don't know N American species. Do you think the OP's tree is P virginiana? Or isn't there enough info. to say?

Looking at the flowers I'd be inclined to call it P. padus. But the two are thought so similar some would have them be a single species.

One of the ways to tell them apart is supposed to be by the surface of the pits (smooth vs. grooved or sculpted).

I think part of any possible widespread confusion may be due to the fact that P. padus is naturalized in North America. People misidentifying naturalized P. padus as P. virginiana may have eventually created an impression of inscrutably close similarity that is not actual.

While P. serotina is related it has definite morphological distinctiveness that should make it easy to keep it separate.

bboy,

if Prunus virginiana is the tree commonly called choke cherry, we have lots of them here in CO. They are like weeds. Although the choke cherry has a similar flowers, it is not as showy as this one pictured. The choke cherry I am familiar with has less flowers in the tree and somewhat leggy statue with significant berries. I understand, P. virginiana may have different variations as well.

So, I 'll have to check the pit later. Which one has smooth pit?

Yes - either padus or virginiana, I have trouble telling them apart as well.

P. serotina is notably different - for one thing, it blooms about a month later than the other two from what I recall. Also, the leaves are less "cherrylike" than most cherry species, longer and thinner, almost more like a peach leaf. Wheras P. padus and P. virginiana have a leaf that is more or less a "typical" cherry leaf.