Curious for holding to buy dips.
Couldn't find anything for bittrex.
Bitterx is having it, you may check here :
https://bittrex.com/Market/Index?MarketName=USDT-BTCAlmost all famous exchange are allowing USDT/BTC trading like Poloniex, kraken, bitfinex, shapeshift,c-cex, liqui and many more. Just google USDT/BTC along with your favorite exchange to find direct url.