Looks like your run of the mill sour cherry to me.

We'll need some images that container more information, strat. Any leaves, berries, or other identifying features?

The leaves look like a Japanese ligustrum. If so, they grow quickly from the berries they produce. They can grow fairly large with a dense canopy, but are weak wooded and have a tendency for the trunk(s) to decay. The berries stain everything they fall on and you will be pulling up thousands of baby trees from those berries.

You are going to find that opinions are like certain body parts...everyone has one, everyone thinks theirs smells great, and that everyone else's stinks. Except, of course, by coincidence, mine. It's the only one you need. You're not so much looking for a specific tree, as a shape. One person will say you need one tree, another will say you need four, someone else will chime in and say only plant in odd numbers, and then someone will ask if a doorway has three sides...and what happens if you have space for six trees, need six to cover the sightlines, but are hung up on the odd number guideline? We're in the middle of an existential crisis...over rules of thumb that just don't matter. Where is the alcohol when you need it? Who says he need to move out from the deck? How do we know what space constraints may exist on the other side? Or what other uses for yard space a person might have? Or what effort a person who has a tall deck to stand on might be willing to put into trimming? My personal recommendation...I'd stay away from trees that have flowers and fruit in areas of high traffic. There are a number of crabapples that would stay narrower than 6-8', but my personal preference, is to avoid the multiple seasons of debris fall (petal, flower fuzz, june drop, fall fruit, leaves all the time) that come with them. Of course, if prevailing winds blow away from the deck, I may reconsider said opinion in this circumstance. So what kind of maintenance budget do you have? Are you interested in something that can be maintained at 2' wide, if you trim it a couple times of year? Any tree CAN be trimmed to whatever size you want...some are more equipped to deal with it. Frans Fontaine Hornbeam is at the top of that list. Slender Silhouette Sweetgum. there are a number of different maples that follow close behind. The columnar maples are more likely to bush out a little more. Given time, anything and everything will want to get wider. Just like people, the waistlines expand with age.