If you can issue yourself newly minted Tether notionally worth a dollar and exchange your own BTC for it on your own exchange it's also dead easy to start pumping the price with wash trades (in theory you could do this by faking USD transactions on your exchange too, and some exchanges probably have done at various periods in the past, but printing USDT would allow you to actually increase your BTC holdings by buying from real traders at the same time, without having to worry about honouring the dollar payments)