The best way to increase your bitcoins is by investing them in different altcoins and with that you will be making regular profits at regular time and it will also help you in multiplying your bitcoins which will eventually increase the level of your coins in your wallet.
This, but to add to this statement I will suggest going for ICO's that's how you get the best price for altcoins.
Yes investing in ico can bring huge profits for you but you need to make sure that you are investing in right projects as many icos have turned out to be scam in the past where only the devs have made money out of it living their investors penniless.
yes most of the time ICOs give good offers, where one can really make good profit in a very very short period of time. because most of the ICOs run for very very short period not more than for some days. and when it is added in an exchange and if the price goes up then it can give you a very good profit in a very very short time.