​I tried to send 0.1 Waves to Bittrex Exchange. I still can't see this transaction in my Bittrex account.

You need to send at least 1.001 Waves, because it is a minimum amount for depositing on the Bittrex Exchange 1 Waves + tx fee. Also It might take some time, it's not instant, for depositing it takes 20 confirmations or about 20 minutes.