Create a New website first then right click on the project folder as shown in figure below.
Click on Add New Item, then you will see a dialogue box titled as 'Add New Item' and you see couple of installed templates as shown in below figure. In that templates if you scroll down you will see Site Map template. Select Site Map template and click on 'Add' button.
After adding SiteMap into your solution. It will generate default code as shown below. and it will be seen in your solution as shown in below figure.