I am looking for a book I read when i was 10, but can't remember its name.
If i remember correctly, the cover was pale tan and had the silhouette of a tree on the front.
Thanks for asking! This one was trickier than I expected, but I think I might have it: take a look at Susan Britton's Treekeepers. Bird, the heroine, takes about the journey you describe (sent to live with a wizard, lifesaving powers of a magical tree) and although that synopsis doesn't mention it, looks like she has an ally/budding love interest named Stoke. Unfortunately we don't have the book in our Omaha Public Library collection, but we can try to find it for you through inter-library loan.
(Side note re: magical tree and sick mother - admittedly, it's such a fantasy archetype that Joseph Campbell will probably materialize out of nowhere and hit me - but I wondered if we might have mashed up some details from C.S. Lewis' The Magician's Nephew. The rest of what you remember reads much more like Treekeepers, but Magician's Nephew really hammers that point about taking the fruit of life with selfish and unselfish motives and the different impact on the eater.)
Anyway, hope that's the one! Please feel free to email back with further questions or call 402-444-4800.