Perhaps this isn't surprising, since the result still talks about an infinite collection of things and Peano arithmetic is not well-equipped for dealing with infinity. However, Friedman managed to produce a finitary version of this statement. Suppose you're looking at a finite sequence of finite trees. Then as long as the sequence is large enough and the number of nodes in the trees doesn't grow too fast as you move along the sequence, you can guarantee that there are two trees with one containing the other.