Fantasy/dreamworld - big tree

Fiction story about a woman who lives a double life - she can go into her fantasy world, but according to her sister(?) she's just dreaming, but to her it's another real world. In the fantasy world there is a big tree - maybe a sacred tree, or a tree that is the portal? She meets many characters in this world, and there's one that becomes a good friend, a male - stocky but small? I have read it within the last 10, probably last 6 years, but not sure how old it was when I read it.

thanks,
Rebecca

That sounds like a book I once read. Could it possibly be The Ancient One by T.A. Barron?

I don't think that is it, but it sounds very interesting too. I believe the character in this is an older woman struggling with emotional issues and I vaguely recall her being in the hospital and her sister visiting her?

By older, I mean not a young girl - maybe late 20s, early 30s.

Parts of your description fit The Witch Queen by Jan Siegel, but I'm not sure it's a good match.

"It is a fearsome world of witches, dragons, and goblins, where a gnarled tree bears fruit of human heads. Fern Capel believes she has left it all behind. But now that world is seeping into modern day England: The witch-queen Morgus, who had imprisoned Fern in the ghostly Otherworld, has returned from countless years of exile beneath the gruesome Eternal Tree. Stalking the twenty-first century in her Prada stilettos, Morgus has the mind-set of the Dark Ages and vows to rule the ancient kingdom of Logrez, now modern Britain.

Most of all, Morgus wants revenge on Fern Capel. Rejuvenated through sorcery, neither charm nor weapon can harm the witch-queen. She has planted a cutting from the Eternal Tree in the real world and awaits with impatience the ripening of its terrifying bounty. When Fern learns that her enemy cannot be defeated through conventional means, she turns for help to her best friend, Gaynor, her brother Will, her old mentor, Ragginbone, and Maldo, the goblin-queen. Together, they track Morgus through London’s high-society parties and seedy, sinister contacts, until they finally draw a magic circle in a Soho basement. Fern Capel knows that survival is not enough: This time she must win. But she does not yet understand how high a price she will have to pay."

No, that's not it...thanks for your help though.

Found it!!! Went over to my friend's house yesterday and she was reading the exact book I was looking for...one I had actually described to her before, but she didn't make the connection. Charles deLint's "The Onion Girl"....finally! She promises to let me read it again as soon as she's done, and in the meantime has loaned me more of his stuff.

Touchstone: The Onion Girl