Because I'm thinking that if i split the budget to multiple coin, risk might be low. 
This might be true, IF, and only IF, Bitcoin is stable, dominance is not too big, and alts can move freely based on their own 'fundamental values'. But most of the time, that's not the case.
If you want to do that strategy, then you have to enter when alt season starts. But that's really difficult, nobody knows when alts can grow without taking any big hit from Bitcoin. If your funds are limited, hold most of your coins in Bitcoin, and only enter alts when Bitcoin is stable.