I find a couple of passages that indicate to me that Gene had moved on in his life and memories of the events that took place at Devon School. Very early in the chapter, Gene is discovering that Devon has been preserved, even after his graduation - both the physical buildings and grounds and the feeling of fear he had known while living there as a student. In thinking about that fear, he realizes "that in the interval I had succeeded in a very important undertaking: I must have made my escape from it."
Upon locating the tree, Gene finds it smaller and less impressive than he remembered it being. He is struck by the change in perspective brought about by his physical growth, by the passage of time, and by the miserable weather, but is grateful to have been able to see it again.
"So the more things remain the same, the more they change after all - plus c'est la meme chose, plus ca change. Nothing endures, not a tree, not love, not even a death by violence."