Quote from contract specs: "U.S. Treasury notes with a remaining term to maturity of at least six and a half years, but not more than 10 years, from the first day of the delivery month. The invoice price equals the futures settlement price times a conversion factor, plus accrued interest. The conversion factor is the price of the delivered note ($1 par value) to yield 6 percent."
So you are not betting on 10 year yields, but a range of yields from 6 1/2 to 10 years. Be aware of that. If you want to bet on the 10y yields in particular, take a look at the Ultra 10 (TN). Their range is from 9 1/2 and 10 years time to maturity.