Friendship is the most visible theme in A Separate Peace. Two of the characters in this story Gene and Finny. Since friendship is based on mutual need, Finny has things that Gene needs and Gene has things Finny needs. A symbol of their friendship is the tree. Jumping out of the tree was something only Gene and Finny could relate to. Jumping from the tree put them into their own separate peace. They lived and in some ways died by the tree.
The first time they had both jumped out of the tree, they went crashing into the clean refreshing water of the Devon River. At that time, they had developed a bond that would stay with them the rest of their life.
One could think that the tree had nothing to do with Gene and Finny's friendship, but without it they would have never developed such a close relationship.
As they jumped off the tree, they were put into their separate peace together.
Gene had a feeling that Finny "wanted to share everything with me, especially his procession of D's in every subject." When Gene discovered this, he jounced the limb when he and Finny were about to jump. Finny lost his balance, "then he tumbled sideways, broke through the little branches below and hit the bank with a sickening unnatural thud." By knocking Finny out of the tree, Gene put himself at separate peace from his fear of being betrayed by his friend. He said, "I moved out on the limb and jumped into the river, every trace of my fear of this forgotten." The tree had control of him.
The tree had control of Gene, Finny, and their friendship. The tree made their friendship possible by giving them something in common only they could relate to. As they dove off every day by starting, the meetings of the super secrete society they were refreshed in a way only they knew about. They were put into their own separate peace together as friends.
From when Gene and Finny began jumping off the tree together, until Finny was dead, they were best friends. The tree is a symbol of Gene and Finny's friendship. As they grew old so did the tree. When Gene looked back at his friendship with Finny, he also thought of the tree. Gene and Finny lived and died by the tree.