However, the real bull run might start in 2020-2021.
How do you know? Just a guess? If the bottom is actually in, which I'm sure not many people doubt anymore, the multi year bull run has already started. It could speed up at some point, but that's something you can't time.
The only thing that matters is to keep holding your coins and to not get excited too early. Most people sell their coins during the first 25-50% increase, which they end up buying back at higher levels because they regret having sold.
I must admit that it isn't always easy holding through price increases, but the initial 25-50% profit during a bull run is peanuts compared to what you can have simply by being patient.