It is one kind of asset. Bitcoin is a popular and valuable crypto currency in this situation. Investment with Bitcoin is a familiar work. Holding is one kind of investment. But we can compare Bitcoin with fiat currency also. Because we can find fiat for exchanging it.
The popularity of bitcoin brings people to invest in it because of the benefits it can give to everyone. Because bitcoin is expensive even though it is volatile which can be a good asset to hold and keep for a long time with a chance to grow because it price increases every year. Bitcoin can also be a currency which can be used for fast and more secure transaction around the world.