There is no "easy" way to earn bitcoin. You have to put effort into earning them, either through trading, working or any other methods. Gambling can be a very "easy" way to earn btc, but you need btc to start off with, and it's very risky, in the sense that you may LOSE your bitcoin.
You can buy bitcoin for money or get other cryptocurrencies in other ways, but getting bitcoin for free for a short period of time is not possible. The value of bitcoin is high, and as the leader of the entire cryptocurrency, it contains more technology than other cryptocurrencies, so getting it is naturally more difficult.