Hop Hornbeam
There are some trees that, once pointed out to you, you'll be able to pick out instantly, forever. It looks unique in some critical way, and you will always know it, leaf-on or leaf-off, close-up or driving sixty miles an hour past it.
This is not that tree.
The hop hornbeam is a fairly common tree in Wisconsin's forests, but it is part of a group of "look-alike" trees that have similar characteristics, especially as saplings. It's known for its strong wood, and therefore it has a nickname: Ironwood. (Same as about twenty other trees, but this is the only one in Wisconsin that's known as ironwood.)
Bark
When mature, the hop hornbeam's bark has a shredded appearance. It looks like a large cat has used it as a scratching post. But saplings and young branches of older trees look very different indeed. These tend to have reddish-brown, smooth bark with a horizontal pattern of breathing holes (called lenticels). These obvious horizontal lines are a birch thing, and wouldn't you know? Turns out hop hornbeam is in the birch family. The twigs are also reddish-brown with little white dots, and none of its lookalikes have quite that pattern.
Leaves
The leaves are a challenge for ID. There are several other kinds of trees that have similar leaves. Touch the leaves; notice that they're not exactly smooth. (They can be smooth on older specimens.) Elms also have leaves that have a fuzzy/rough texture, but in elms, where the leaf joins its stem, the two sides of the leaf are different lengths. So it feels like an elm but it isn't one. The other tree that looks similar is the other hornbeam, the American Hornbeam (aka blue beech, aka musclewood), but AH has a bit more blue in the leaf, and the bark looks like muscle. Hence the nicknames for AH. Also, HH has short, hairy leaf stalks, so look at that too.
Fruit
If you're lucky, you'll see this tree in fruit. The fruit look like bunches of flattened pouches, not unlike how hops look. Hence the name "hop hornbeam." Oh--the "hornbeam" part comes from its historic use in ox yokes, in case you were curious. If you do see this feature, you can be very certain of your ID. If not, you can be like me and stomp your feet, beat your chest, check six different field guides, and pull your hair out trying to decide which of several visually similar trees you're yelling at.