Originally Posted by meow meow
Try playing with a string with him. If you dangle it at the top, I bet anything he will go there.
My kitty likes the top the best (probably away from my two kids!).
Great answer! Dangle his favorite toy on the top bed and he'll go after it! Once he's up there, continue to play with him with his toy. Also once he's up there, you can put his toy away and just stimulate him by scratching underneath the bunk.
Is your tree in a window with sunshine? They prefer that the best! But if the top beds are above the window line he'll lay on the lower beds preferring the sunshine over the top beds.
You can also entice him with catnip leaves or spray.
I also agree that the tree has to be sturdy. We bought one of the biggest, sturdiest ones I could find. My girl has no problem with it, she's 10 lbs. Her twin brother is an absolute MONSTER at 17lbs (and still growing according to our vet!) and he shakes that thing like no tomorrow.....but he still loves the top bunk lol.
Just wondering if Oscar has a playmate? Most cats love to climb on the beds and "bat" at each other playing as they romp around. If he's single, he may just not be sure what he's suppose to "do" with the tree. If you play with him on it, he'll use YOU for entertainment (not you physically, I mean with toys) then and soon you'll find him jumping up there and rolling around when you are in the room, waiting for play time!
This is all I can think of, hope it helps.