My brother posted this picture from his yard asking the title question. Does anyone know what the fruit is?
I'm pretty sure that's Autumn Olive (Elaeagnus umbellata)
The bark, leaves, and the coloration and surface texture all line up with what I would ID as an Autumn Olive - not to be confused with Russian Olive. Russian olive fruits in spring, but Autumn Olive fruits - well you get the idea.
My only hesitation in this ID is the time of year of the photo. It is WAY too early on the east end of Long Island for there to be ripe fruit on an Autumn Olive. Is this photo from last year, or is it from a more northern climate?
EDIT: Autumn Olive is a nice and useful edible fruit (make sure you have a positive ID before consuming). The sweetness of the ripe fruit varies widely between plants and even year to year. So you may find one that is super tart even late in the season, while the next plant over is producing really sweet fruit. A quick google search for "Autumn Olive edibility" will give you plenty to work with.
They look like cherries, but I wouldn't take my word for it. I always remember the rule of thumb, don't eat red fruit you're not sure of.
Does this fruit have one large pit/stone or something else.
One thing that makes me suspicious is that the fruit is still on the tree. When I had cherry trees as soon as the fruit was ripe, the birds would eat them up.
So, they might be cherries. The fruit looks right, the leaves are close and I can't really see the bark clearly. Good luck! I hope it's a cherry tree.
It looks like Choke Cherry. This Pinterest page has some pictures and information.
This is what they call a pie cherry. The cherries are bitter not sweet. Birds still love them and they are wonderful for pies, thus the name, as long as sugar is added. Does this tree have thorns? I am unable to tell for sure in your picture. Your tree does need a bit of thinning and we can guide you through that process as well. Have you tasted one of these cherries? Not at all poisonous.
Wait a bit to allow others to chime in with their thoughts. I am ID ing as Prunus cerasus or Tart Cherry. Prunus cerasus