You can buy bitcoin from the profits made through selling bitcoin, but even if your long term goal is to buy and hold bitcoin, don’t buy any altcoin unnecessarily without proper research. You should also have a clear exit strategy so that you can sell the altcoins at the right time and save yourself from going into loss. I prefer to buy bitcoins when there’s a dip. I don’t wait for the price to go very low but if it goes I buy some more.