Cherry Tree problem
Hmmmmm.... I think that those are galls on the leaves. Is it happening on many leaves or just a few? What kind of cherry tree is it? I have never seen this issue in commercial cherries, but I think that the galls are harmless unless they are on the whole tree and you have no good leaves. Galls are often caused by arthropods, and this one is probably an eriophyid mite.