Probably is still fermenting, just because it's not bubbling doesn't mean things aren't happening.
You don't likely need to add more yeast; if you have some nutrient that would be a better addition. I always add yeast nutrient to my ciders, helps them finish off nicely.
Also, unless it ferments dry and you backsweeten you're risking bottle bombs. Look up lots of articles on making sweet, carbonated cider. It's not as simple as you may thing.