Every decision is in your hands, I do not recommend buying bitcoin in large quantities when bitcoin is at a high price, there is no certainty that the bull market will make you a big profit from buying bitcoin. My suggestion is to exchange the altcoin you have for Bitcoin then save it until bullishness occurs again this year. If this is a good start to your decision, do it in principle in your own way.
Every decision is in your hands indeed and this one too has to be carefully planned out for it to be a profitable investment, otherwise it might just be another case of trial and error that led to more loss of coins and investment.
In accumulating the profits from altcoins and DCAing for the duration till 2030 as stated, it may not matter the price of BTC if it is bought in fractions and kept, whether we enter the bullish or bearish season, until one decides to sell or diversify further to accommodate other investment.