After you've clicked Add to Quote, you should get the standard pop-up for your cross-sells. You can see common alternatives for your tasks also if any and they can be directly added to Quote as well. You can change the alternatives to an Add-on as well by sliding the toggle as can be depicted in the image.

           
By default, cross-sells as treated as tasks. But, if you click the toggle in the top right hand corner of the box, your screen should look something like this:

This functionality is helpful for making sure you pricing works out exactly the way you want it to. We don't want you to overcharge, or undercharge, your customers in any situation.