Definitely ash, and very likely green ash. These are street trees and from my own work, I know that green ash was an absolute workhorse tree for such applications for a couple decades following the demise of the American elms. Not just as replacements but for general planting of streets in new subdivisions or whatever. Monoculture as applied to plantings of this sort are entirely appropriate. It's easy to dismiss this practice now that emerald ash borer is in the area, but the range of choices available to municipal foresters can be quite limited, once all factors are considered. Green ash would grow anywhere, in any soil/moisture condition, and grow fast to boot. We quit working with all Fraxinus more than ten years ago, as EAB showed up on the horizon. BTW, if that pic is in SE Wisconsin, those trees are truly threatened by this insect. That's the area where it has invaded the state first and most heavily so far. For my tastes, I'm really going to miss white ash. They're one of my favorite northern hardwood species. But even these green ash had their good points. It was always kind of easy to take them for granted, but no longer. +om

Actually, this evening I walked back into the woods behind my property and found a similar elm, about 50 feet away, but not in sight of this sapling. So I'd guess that was the source. I know it would make sense to replace it with a better elm, but in fact, I wasn't planning to plant an elm there at all. I already have enough big trees around, so if I removed it, I'd plant other things there. Guess I'm just looking for a rationale not to kill it.

The property that used to be my Grandfather's place has some 100 year old plus elms, all americanas. We are in the Gulf of St Lawrence, so get LOTS of wind and freezing rain. They have stood up well. Some have died of the DED, but two are thought to be resistant. Since the current owner is injecting them with fungicide and has used Dutch trig, it's not known for sure if they are resistant, but their buddies started dying off fast and these two appeared to wall off small amounts in the crown. I have some of their seedlings, but suspect they are pollinated by their non resistant buddies that survive with treatments. A kind soul on this board has sent me seeds from his resistant trees, and two have made strong seedlings. It will be fun to plant them next to the Elmwood 18 seedlings and see what pops out. I still have my grandfather's woods, and there are elms there, so I am hoping to introgress resistance genes into the population in the woods. I haven't actually seen a Valley Forge, only its seedlings, so can't comment.

this is the type of tree.. you learn a very valuable lesson on ... you should not have bought this particular tree ... because of this ... and trust me.. i bought a lot of trees... before i learned this lesson ... your second lesson.. is that when this thing is a foot or 2 thick .... this wont matter ... part of you stress here.. is you want it perfect now ... and wehn pruning trees... now is not really a big deal.. most deal in centuries ... i had a situation like this.. and it took me 6 years.. to clean it up ... yes.. 6 years ... and you want to know what need be done now ... the consensus seems to be.. take out the middle one... i will leave it to them.. as to how to do it ... because i never figured out how ...... look close at the first pic ... do you see those raised areas in between the trunks... that is the fail point .. at some time in the future ... as those trunks thicken.. they will include bark.. and create a horrible crotch ... see link.. especially the 2nd and 3rd pic https://www.google.com/search?q=included+bark+in+a+bad+tree+crotch&source=lnms&tbm=isch&sa=X&ved=0CAcQ_AUoAWoVChMImdPk5ez0xwIVkxGSCh0MzA4r&biw=868&bih=745&dpr=0.9 then come back in a year or two ... just never forget ... there is no real hurry when pruning ... also ... get a good pair of hand shears ... i prefer felco ... if you had snipped this problem out.. 3 years ago .... because you saw what might come of it... then we wouldnt be here today ... gotta run ken