In Chapter 2 of A Separate Peace, Gene comments that since some boys are too young to be drafted, that they and school itself are a symbol of peace, which is contrasted with the war. The idea of the school as a haven of peace is underscored by Finny's youthful innocence and how he can get away with anything. It is such a place and time of peace and protection that they are even beyond the reproach of teachers.
The tree limb from which Finny falls represents a literal and figurative balance between peace and violence (and/or war). Finny sees the tree as an instrument of innocence and adventure, but it becomes a symbol of that balance between innocence and responsibility. This is a parallel with the boys themselves, being 16-18 years old, on the cusp of adulthood and some also on the cusp of entering the war.
In Chapter 11, Brinker drags Finny and Gene to the Assembly room where 10 classmates are there waiting in their graduation gowns, looking like judges or members of a jury. This is the first blatantly public exposure about the possibility of Gene's wrongdoing. Finny leaves the room in a rush, unable to accept or acknowledge that his friend could do this just as Finny is unwilling to grow up and/or accept that the war is real. This scene obviously resembles a courtroom where Gene is literally to be judged by a jury of his peers.