We have an artificial tree with light bulbs already attached and my cats keep getting underneath it and rubbing and chewing on the light bulbs
How can i stop them from eating them

I have the same problem with my ferrets all you have to do is buy something called BitterApple at the pet store it comes in a cream and a spray its made for animals that have chewing problems animals dont like the taste of it
the cream will last longer on your cords than the spray will but if you can only find the spay it will work just fine you will just have to apply it more often

lots of cats and ferrets

ahahaha that's cute!
All you can really do is tell them not to do it .

Animal Lover !