Normally either bitcoin is moving up or altcoins are in positive direction but not both. Last few days are especial in a way that both bitcoins and altcoins are moving up. i didn't see this trend before. Maybe it is due to year end where all the coins close at a high each year. Last year we say bitcoin reach 1000$ which was all time high at that time.
In the spring of 2017, too, everything grew, Bitcoin and Altcoins. It is difficult to predict what will happen next. In the last days bitcoin falls, altcoins grow. Therefore, it is better never to sell all bitcoin in your portfolio. Diversification of risks should always be.