If we talking about big investments (100 000 $ for example)
Can i be sure that in a 5 or 10 years, btc will go up or stay same as today?
no, you can't be sure. if you could be sure, then bitcoin would already cost 1 million because all the world's money will be poured into it. the only reason they are not is because you can not be sure at all.
There is one thing you can be 100% sure about, though. It's that in 5 to 10 years the price would not "stay same as today". it would be either many times more or close to zero.