I've had apple trees and crab apples, too, but I've never seen a squirrel in one. In my part of the world where nut trees are among the most common trees (oaks and hickory trees especially) one would never expect to find a squirrel in an apple tree. Thank goodness! I'd hate to think the squirrels would eat my apples!

I should have added that we have very few red squirrels in the US. We have three types, the eastern gray squirrel being the most common, followed by the larger fox squirrel (gray with a red tail), and up north we have a very aggressive squirrel known as the black squirrel, which is a smaller cousin of the gray squirrel.