svk, if you're in Northern Minnesota, I doubt you have bitternut hickory, not impossible, but extremely unlikely, as I didn't think that tree grew that far north in the midwest. I've been cutting trees in the U.P. (basically the same country and latitude as you) all my life and have not seen a bitternut hickory until 16 years ago when I bought the land we're living on now here in Wis. In fact, this was the only tree I could not identify in my woodlot after I purchased the land; my brother in law is a forester with working range in the U.P. and upper half of Wis. and when he cruised my woods about 10 years ago I walked to the largest hickory, pointed and said "what tree is this?" and he had two guesses and one was bitternut hickory, evidently he had not seen any or many of these either. What clinched it years later was talking to a guy at work who gave me a cubic yard of hickory chips for smoking meat, the chips came from his firewood business (he gets tops and culls from his sons' logging operation). I described this mystery tree to him...I said the bark is somewhat smooth and looks like wrinkled boot leather and right away he says bitternut hickory.....when he loaded the box of chips onto my pickup he tossed a split from a hickory round on top of the box and asked me the next day if that was the tree I had in my woods and I said that is exactly it.
At this point I'm guessing soft maple (aka red maple) because: 1) they tend to grow in clumps (you mentioned these are growing in a group), 2) and, while the pic of the tree on the left does not readily appear as soft maple, the pic on the right is a dead ringer for it, and 3) you referred to a reddish bud on the twigs - another sign of soft maple. I have a lot of soft maple as well as bitternut hickory in my woods and a lot of the maples are part of groups of up to five or six trees together while I haven't seen any hickories in a clump, at least not here. If you had more pics of all the trees in that group and a pic or two from 6 feet or so away as well as pic of the entire tree to the top, that would shed more clues.