Hello. Happy to help.

The tree in the photo is really an eastern red cedar (or juniper). These slimy growths are one part of a two part system called cedar-apple rust. For this entity to complete its lifecycle, it requires a juniper and an apple tree that are within a few hundred feet of each other. They do little harm to your tree so we don't recommend any treatment other than pruning off the galls and witches brooms.

If you have an apple or crabapple nearby, then you may want to see how it is affected and take action there. If you don't have an apple, then it may be on a neighbor's property.

Here is more information about cedar-apple rust from the U of MN Extension: https://extension.umn.edu/plant-diseases/cedar-apple-rust#managing-rust-on-juniper-and-eastern-red-c...

I hope this information helps.