I believe they are tent caterpillars!!! Get them out of the
tree, they eat every last leaf on the poor thing!!!! I hate them!! and that's a strong word for me to use!!! HATE THEM!!!!
anywho.....the ones that are up, out of reach i wrap an old rag around the end of a pole, I know most of you will be upset by this, but I am very careful when I do it, put a few drops of lighter fluid or something to have a small flame and burn the "tent" out of the higher branches. You don't burn the
tree, just get it close to the web and it melts away and the caterpillars drop down and you stomp away!!! They really are devastating to the foliage esp. on a young
tree. Anywho... get them out! Yuck! Good luck!