Although we can't identify the exact cause of the branch dieback from the photos, causes of sap oozing (called gummosis) include general stress, injury, infection with fungi or bacteria, and wood-boring insects (which usually target trees already under stress). We recommend the tree be replaced, in part because there is a lot of lost growth, but mainly because it has poor branching and because the tissues oozing sap may already be too damaged to salvage. The branch structure is poor because the main branches should not be this crowded (originating almost on top of each other where they attach to the trunk) and they should not cross over each other where bark rubbing or branch fusing could occur as they enlarge over time, because this makes them vulnerable to infection or storm breakage. Branches with a narrow crotch angle (the point of attachment to the trunk or a larger branch)  are also inherently weaker and more likely to break in strong winds or due to slow/ice load; one of the branches that appears to be curving into the canopy looks like it has a very narrow crotch angle, and the nursery growing the tree (if this was recently planted) should have pruned that off well before it became that large.

For future reference, do not seal or treat a bark wound with anything because those products do not help the "healing" process and could actually do more harm than good. (Plants cannot heal in the same way we do from an injury, though they do have ways of defending healthy tissues from invasion by pests or disease so the injury does not worsen. As can happen with people, though, this doesn't always work and sometimes too much damage was already done to vital tissues.)

Copper fungicides can be useful broad-spectrum treatments for a variety of diseases, and it is one of the only fungicides that has some impact on bacterial pathogens, but no fungicide can cure existing disease; they are only used as preventatives well before any symptoms manifest. Even if this tree was being kept and rehabilitated, sprays applied now will not have any benefit. If used in future years, heed any precautions on a copper-based pesticide product regarding application frequency because there are limits on how much copper can accumulate in the soil any given year before it causes harm.

Similarly, even if the tree was treatable, cutting off all branches is not going to result in healthy regrowth. While otherwise-healthy trees can regenerate some of their lost canopy, the branch attachment points of those new shoots are almost always poor and they will be as vulnerable to infection or weather damage as the branches they replaced, if not more so because they are secondary growths.

When planting trees amid lawn, we recommend the base be encircled with a zone of mulch do keep the grass from growing too close to the trunk. Not only will this lessen some of the competition the grass has with the tree's roots while it is still establishing, but it will act like a buffer against accidental trunk strikes from mowers, weed-whackers, or the application of any herbicides, all of which can cause serious and fatal damage to tissues just underneath the bark. You can learn more about proper tree planting depth and other important measures on our Planting a Tree or Shrub page.

If this site is predominantly sunny in summer and the soil drains well (since cherries are intolerant of soggy soil), you can replant another cherry there if you want. Select one with branches spaced further apart (both vertically and around the trunk) instead of being clustered together, and whose main stems all head away from the center of the canopy. Any branches that cross over atop others need to be removed, though cuts need to be made carefully so they don't damage the tissues at the branch base that seal-over the wound. Ideally, this is something already monitored for and taken care of by the nursery.

Miri