When I was younger, I loved The Giving Tree because the entire book was and still is one big Crowning Moment of Heartwarming. Throughout the book, the tree calls the boy "Boy" even after he grows up and becomes a teenager, a man, a middle-aged man, and an elderly man. I didn't understand that until I realized that it was the tree's way of indirectly saying, "Even if you're too old to spend time with me anymore, I'll always see you as but the little boy that used to swing from my branches and eat my apples and nap in my shade." Awwwww.
I also loved The Giving Tree when I was younger, since I loved the fantasy theme of a senteniant tree communicating with a boy. I realized that the book is a metaphor, as well as satire of the progression of a sex-oriented heterosexual relationship. The boy represents a man who never tires of his sexual endeavors, while the tree represents a woman who starts to lose her interest over the course of their relationship. The tree becoming a stump is a metaphor for a woman who has nothing left to give to her hedonistic partner. The old man represents the man who still gets a thrill out of his sexual adventures.