Hickory tree has strange bumps on the leaves.
These are probably leaf galls, which are not usually a disease, but the reaction of the leaf to activity by insects, mites, etc. There are many, many kinds of galls that appear on many species of trees. The vast majority of them are harmless. Here is information from our website: http://extension.umd.edu/hgic/shade-tree-galls
You can search 'hickory leaf galls' online if you want to find the type of gall your tree has. You can also send us photos to id.