The tree in the novel A Separate Peace, written by John Knowles, represents a great deal to Gene. The tree's appearance changes both physically and metaphorically throughout the course of the book as Gene gradually matures into an adult.
The tree is symbolic of good and evil, as in The Garden of Eden, when Adam and Eve give into the temptation to eat of the forbidden fruit. Just as the tree is symbolic of good and evil in the biblical story, Gene gives into the temptation to hurt Finny. The tree appears as an unwieldy beast to Gene, and serves his jealously well as he pushes Finny from the limb. It represents a choice. Unfortunately, Gene chooses evil, thereby injuring Finny and ruining his athletic aspirations.
The tree also is referred to as artillery at one point in the novel, representing the ominous rise of World War II on the horizon. This is a similar representation to the above tree of good and evil, as the tree is compared to weapons of war. It is a turbulent time of both adolescence and the cusp of manhood as the boys ready themselves for the inevitable enlistment in the troops, and the inevitability of growing up. In youth, Gene sees the tree as menacing, and as a tool to do his bidding borne of jealousy.
Later, as Gene looks back at the event as an adult, the tree seems to lose its threatening appeal, and Gene views it as an old, shrunken relic of a lost time. It poses no threat to him at this point, because the deed has already been done. Gene must reconcile himself with his actions. He must come to terms with Finny's death and his part in that tragedy. In the end, the tree is simply a representation of life gone by and old wounds. The tree is indeed like the discarded war artillery as well. War is over, and the tree stands alone, just as Gene must do as an adult coming to terms with his behavior at Devon and the loss of Finny and the over-reaching theme of innocence lost that runs through the novel. The tree, ultimately withered and old, is indeed a separate kind of peace for Gene. He is now free of its terrifying hold.