Wow! That cat tree is gorgeous. I would have never guessed that it was home made. Your father is very talented. I'm so sorry to hear that he has Alzheimer's though. At least he was able to make this for you before he got too bad. I'm sure you'll cherish this forever.
I hope you'll be able to fill the fourth cat spot on your tree with another cat. I now have four, which is the most cats that I've ever owned at one time, and I think it's a great number because they each have a buddy. Good luck.