We have a full grown 9 pound cat. He has some disabilities using his front paws so we made a few modifications in this tree to fit his needs. 
One photo shows the way it was designed to be, he was able to get up to the top but getting down was his problem, so we made more flat surfaces for him to climb down. If he has to jump down from tall places he lands on his face. The modifications also gave him great places to sit and watch out the window. 
 I love the fact that this is some what modular, with the cat's help it took less than an hour to put together.