Currently, we need to define legend by hand. Add a patch (like [TreeReader_TwoDPlots.C#L17-L25](https://github.com/ram1123/Plotting-Macro/blob/3bfec83dfc042f500bc376f00ad59e4d7b913de7/TreeReader_TwoDPlots.C#L17-L25)) so that it can take legend automatically.