Thanks for writing in with your question. I’d recommend focusing on gaining STRENGTH and not muscle mass. A max strength based approach should see you able to improve your pull ups. A mass gaining approach is less likely to do that. Adding mass will mean that you have a heavier body to pull up to the bar. So you will have to gain more strength than you add in mass.
Look at the best rock climbers who have very high levels of pulling strength and they are all quite lightly muscled and lean. Contrast that with an NFL lineman who have lots of mass and many can’t do a pull either.
Getting past the first pull up is the hardest part. The way we usually help folks with that is by having them get on a stool to get their chin above the bar as a starting position. Step off the stool and hold this top position for a count of 3 if you can and then slowly lower to a count of 5. Repeat this 4-6 times with a one minute rest between each rep. Do this 2x/week. Time under tension is a great strength stimulus. You may gain some muscle mass in the process but that will be a side effect of the strength.