Stinking cats!! 😾

Christmas I coming pretty quickly. Our house is not big enough for a full size Christmas tree. So we just take the top and do this with it.

However, my cats love to climb up into that window now and I'm worried they will tip over and destroy the tree. I need some ideas on how to hopefully teach them to stay out of the window and off my table. Please help me and give me some ideas! I really want to be able to have that tree up.