Once you installed Visual Studio 2013 and tried building a custom Outlook add-in you will the see the Outlook 2013 add-in template available.
Recently one of my customer asked, what if he wants to build Outlook 2010 add-in and he failed to see the respective template for it.
I suggested the following steps to try, which helped him to move forward.
Steps to try:
At Visual Studio > select New Project dialog > change .NET Framework target version to 4.0 > now you’ll then see the Office 2010 project templates. (below is the snapshot)
Hope this helps.