As an adult and an alumni, Gene searches for, and eventually finds, the tree that was the location of the central event of the story and, in fact, of his entire time at Devon School. In Chapter One, the full significance of the events that took place there are not explained, but its importance to Gene is made very clear.
This was the tree, and it seemed to me standing there to resemble those men, the giants of your childhood, whom you encounter years later and find that they are not merely smaller in relation to your growth, but that they are absolutely smaller, shrunken by age.
As the flashback begins, Finny is daring Gene to climb the tree, an act that appears large and somewhat forbidding, beyond the fact that Upper Middler students such as Finny and Gene were not allowed to climb it according to the school's rules. Already, Finny is being presented as the charismatic ringleader, unafraid to challenge authority, unconcerned about consequences; already, Gene is reluctantly following Finny's lead, hating the doing of it, not understanding why he went along with Finny's ideas but craving his approval.
"Come on," drawled Finny from below, "stop standing there showing off."...What was I doing up here anyway? Why did I let Finny talk me into stupid things like this?...With the sensation that I was throwing my life away, I jumped into space...immediately I was on the surface being congratulated. I felt fine.
The conflict within himself that creates the driving tension for Gene throughout the story has now been presented to the reader. The tree is the catalyst, the symbol of the unacknowledged competition.