Briefly, ebooks-tree.com seems to be scraping content from a lot of sites without the author's permission. They are apparently charging for downloads, or intend to (not entirely sure how this works, I downloaded one title without paying) so there's undoubtedly a royalties issue etc.
This blog post describes what's going on and how to complain:
On a quick check I noticed, for example, that they have 11 titles by the late Aaron Allston including Star Wars books, I have no idea if these were on line as freebies or have been pirated, but I doubt that they were put there with his permission. Ditto a lot of autopope's books.