You don't have any reason here, if altcoin price up then bitcoin will up as well, I have a reason for it. Because bitcoin will be choosen first by investor. Before they have intention to buy more altcoin they will buy bitcoin to avoid losing all their money. You may see how the prices altcoin are, was pumped drastically and need a few times then you will see their prices will go back to original prices even lower than that, and this thing will be a high risk for them. You have to consider your portfolio first before decide to choose some altcoins, think carefully about your risk management and you will be safe.