We have a tall cat tree, and 2 shelfs:

https://www.amazon.com/gp/product/B0711DDCR1/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

https://www.amazon.com/gp/product/B0091OMWUW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The shelves are mounted so they can easily climb out to get higher. It’s no uncommon have 2 of the 3 sleeping on the tree in the afternoon.