You have lots of options, everyone. Black Tree is now available in paperback, hardcover, and as an eBook. So take your pick of what you like best. A simple paperback, a sturdy hardcover, or an on-the-go eBook.
You can also buy it from your favorite source. I recommend Lulu. Or you can buy from Apple iBooks, Amazon, Barnes & Noble, Book Depository, and a few other places. Remember, Book Depository offers free shipping worldwide; at the moment, they're only carrying the paperback, but the hardcover should be up, too, soon.
If you're an eBook-lover, you're in luck: Barnes & Noble has the NOOK edition on sale right now. Click here to get it now.
And if you'd like a taste of the book before you buy it, click here to read the first chapter.