Unconditional Love
Interpretations from the tree being a symbol of the boy’s mother to the tree being a metaphor for Christian charity are all applicable to the theme of unconditional love. The tree consistently gives the boy whatever it asks for, never asking for anything more in return than love. This fits in well with a mother’s unconditional love and with the idea that charity should be equitably delivered to all who need it, regardless of their own character or lack thereof.
Gender Roles
The tree is referred to as “she” and “her” and calls the forest her home. While the tree never gets to leave her home, the boy gets to leave home and find a job, marry, have kids and even set sail for a sea voyage. All the elements associated with the boy are related to gender expectations of males while the all the gender expectations of females are situated within the tree.
Environmentalism
Little by little, the boy takes more and more from the tree until by the end there is nothing left but a stump. And then he comes back to take advantage even of that! The story can be interpreted as one in which the overriding theme is the exploitation of natural resources to fulfill the short-term selfish desires—the wants rather than the needs—of human beings who take no responsibility for renewing the resources they have destroyed.
