We put in two serviceberries on a bed that is about that width. I have seen them grown up in a landscape at our bank, and they seem like they will be about right. I think they fall in the "aboreal shrub" category, because their trunks are branched down low, but they get tall enough to look like a tree.

Morning Oswegian,

Thanks for your suggestion. Going to Jamaican Gardens in Morton Grove to look for a service berry tree/bush. Thanks again, I'll let you know what I find out.

TCG

Try Lurvey's on Dempster by 294. Good selection, prices and helpful. I also like serviceberry.

How about a Smoke Tree? How tall are u looking for? Toni

Thanks so much for the input. Going up to Lurveys this afternoon, checked out its web site, looks good. thanks Robarba. Toni, looking for a tree in the 25-35 foot height. Not familiar with a smoke tree but will make inquiries. Thanks again!

A 7' width is not much to work with.

Parrotia persica 'Vanessa'
Amelanchier 'Rainbow Pillar'
Fagus syvatica 'Red Obelisk'
A fastigiate hornbeam would be a good choice as well.

Sounds like you would be ever so much better off with a section or two of tall lattice fencing arranged in an off set way... vv or /// (sorry, I cant find a symbol to show what I mean) Anyway, you wouldnt have to worry about the underground pipes, roots bulging up your respective driveways or a too-agressive plant. Also, both you and the neighbors could plant vines or hang baskets on the fences.
The conifer forum lists some tall and narrow arborvitae trees if you really want to go with trees. Both of my suggestions might cause problems about where to go with the snow banks in winter.
I have a narrow tree called the sentinental maple that grows in the narrowest part of my lot line. The branches stay in an upright position. However, it still rains a ton of leaves onto the neighbors yards in the fall. Not sure they are keen on that. Maybe talk it over with the neighbor and see if they have any ideas.

Pondy

Serviceberry popped into my mind right away too. (Maybe because mine are budding out today.) Serviceberry is a native, provides food for wildlife too, which is a nice bonus. It goes by many names, Amelanchier is the Latin name. Good luck!!