I know that long-duration bonds, on a a single bond basis, exhibit convexity. However, do Treasuries futures prices and the 10 year yield exhibit the same property?
Below is a plot of continuous 10 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??