Here are a few cat trees that I have seen on the web. Sadly I do not recall WHERE on the web I saw them (so if any of these pics are yours, please tell me, and I naturally will give you the credit that is due to you!).
I thought this one was a great space saving idea, and cute to boot! :)
This last one is considered to be the LARGEST Cat tree in the world, and ia at the Angels for Animals in Canfield, Ohio, U.S.A. They are like the SPCA, also is a not-for-profit animal adoption center, and I added this one because it it HUGE and simply amazing!
I also have made my own cat tree using recycled materials, you can read about it here: http://fine-frugality.blogspot.ca/2012/03/diy-tuesdaya-little-late.html , along with pictures and such for extended understanding here: http://fine-frugality.blogspot.ca/2011/03/april-article-picture-additions.html hope you all enjoy! :)