As has been said, simply cycling will only add a small amount to muscle mass. Go to the gym if you want tree trunks for legs!
Frankly, I'm a mere mortal and I don't want huge legs. What I do aim for is to be as good as I can be on the bike (speed/stamina). That means lots of miles, hills, and the right(ish) diet. High protein , low fat.
My only concession to mass/recovery is creatine supplementation.
For me, I found tweaking my diet made a noticeable difference.
I do about 110 commuting miles and regular weekend rides of between 15 and 60 miles.
As an aside, I went through a short phase after watching a few of the Alpine events online of just climbing my local hills, it's fairly flat round Outer NW London, multiple times to get a feel for what a big climb might be like. Getting out of the saddle realy does work those quads/glutes out!