recipe ended up too bitter.?

I braised pork and celery added to the top. I do not know celery cooking for an extended period of time, tastes bitter. now it tastes too bitter! Does anyone know what to add to act against bitterness, for example (adding sugar to balance too much salt) thank you

parsley may help take some of the bitterness Out. It is good to absorb strong flavors like onion, garlic .. morning breath .. .. can not be wrong to try to celery. It gives little flavor of its own