The only thing I’d like to add to what Al said is that one leg deadlifts can be great for stretching the hamstrings, as well as providing an excellent antagonistic movement to the pistol squat. If I were to do 2 leg exercises, it would be these two. Progressively, you will want to have less and less bend in your knee until you can do it with your knee completely locked out…which should not be approach haphazardly. It can be dangerous for the knee, especially if you are picking weight up off of the floor…but if you can safely get there it will be great in building strength and stability in the knees. Some people will never get there, and bending the knee is fine as long as you are able to keep your back straight, shoulders back, hips level, and feel the stretch in the hamstring and the power of the movement in the hip and hamstring. However, the great thing is that one leg deadlifts are much more approachable than pistols so you should be able to start doing them already. Plus, it being a unilateral movement, can only help your bilateral deficit.