There is minimum or we can say zero risk involved if we talk about investing in Bitcoin. It's just an inner fear or trust issue which one has to overcome and start investing in Bitcoin, rest is a smooth journey. We have discussed and seen many cases of investing in Bitcoin for longer duration, as long as someone intent is to HODL Bitcoin for 5 or more years he is bound to get good return.
It's important to keep investing in Bitcoin the discretionary income we have in our hand. If someone don't have any discretionary income for Bitcoin then he must think of how to generate that discretionary income.
Minimum risk is possible for the long term but not risk-free or say 0 risk when it comes to bitcoin.
Everything has a risk especially when talking about bitcoin so we cannot say risk-free bitcoin even 0 risk even if it is done for the long term even though bitcoin is still very worth it to do.
In this context for the long term we actually only minimize risk because at least with the long term our risk will be smaller than for the short term but that does not mean this is 0 risk because after all when we talk about bitcoin and invest in it there will be no such thing as 0 risk. Don't because we are too sure that we forget or eliminate important things as if it were certainty even though risk is quite closely related when we are in the scope of bitcoin.