I know long duration bonds, on a a single bond basis, exhibit convexity however do treasury futures prices and the 10 yr yield exhibit the same property? Below is a plot of continious ten year treasury futures (ZN contract)since 2003, where the Y-Axis is the price of ZN futures and the X-Axis is the yield/interest rates on the 10 year. While there should be a non-linear relationship between bond price and yield for a single bond, that doesn't seem to be the case when looking at the futures price/yield relationship. Why??