The clumps on the branches of your Pin Oak tree appear to be oak galls. Galls are irregular plant growths which are stimulated by the reaction between plant hormones and powerful growth regulating chemicals produced by some insects or mites. Galls may occur on leaves, bark, flowers, buds,acorns, or roots.Leaf and twig galls are most noticeable.The inhabitant gains its nutrients from the inner gall tissue. Galls also provide some protection from natural enemies and insecticide sprays.
You can find more information in the University of Kentucky publication:
"Common Oak Galls"