Just buy bitcoin while there's still a time to buy and the price isn't reaching more than $20,000 or when you want to invest when the price is $100,000 already? If you think that bitcoin will be dropping to altcoins price at the end of the year, don't think about it. Price of bitcoin is about to surge most of the time so if you don't want to be left behind by this express train, get in.
Besides even if that were to happen that does not mean that altcoins are going to remain in their current levels of market capitalization, if bitcoin crashed then all alts are going to crash as well since there is going to being a stampede to get out of the crypto market before it is too late, so to think we can reach those prices and that there is not going to be consequences for alts is a mistake.