Answer:
There is no more of a reason to hide that you are a bisexual person than to hide if you were gay or lesbian.
But if you feel you must hide or be "in the closet" for some reason, there is the idea that it is "easier" to hide being a bi person because all you need to do is date/marry people of the opposite sex and never tell anyone. But -- and this is a big but -- being in the closet and lying about who you really are is no eaiser for a bi person than for a straight or gay person. The closet distorts your heart and mind and makes you less of a person and can damage the way you learn to love and accept others.
Also, you may be capable of only expressing your love in a heterosexual-style relationships but -- what if you don't really love that person? What if "the one for you" turns out to be a person of the same gender/sex as you? Then forcing yourself to stay in the closet will be hell.
If you do genuinely fall in love with someone of the opposite sex, it may again seem you are on easy street and can just never tell anyone you are bi. But a person's sexual identity is not just about who they have sex with, but is also part of how they see the world and express themselves in it. You can be entirely monogamous, in a relationships with an opposite sex person, seem like a straight person to everyone, but if you are not fully expressing your mind, heart, soul and opinions by forcing your full identity into a closet, you can still live quiet an unhappy existence. I'm not saying a bi person should never settle down in a straight relationship -- by all means, if that is your true path, absolutely! But not by lying about who you are. It's the hiding and lying about your identity that can distort you. A bi and straight person can be very happy together, but should be able to speak their own truths and express their minds and hearts fully. No lies.
[Previous answer: I'm not sure why you would want to hide it, but bisexuality is probably the easiest to hide. Just don't tell anyone. Date only people of your opposite sex. It wouldn't be difficult since you truly do like the opposite sex. Don't make comments or hint at the fact that you like the same sex. Just basically pretend your straight. I think you should come out though. it may be hard, but screw anyone who doesn't accept you.]