You can assign server instances to server groups when you first register them, or by modifying their properties afterwards.
NOTE:You can group server instances in the navigation pane tree based on their category or server group. Categories are similar to server groups, but they offer different features. For more information, see Change Server Instance Grouping Methods.
To assign a server instance to a server group
Select the Backup Manager pane (CTRL+1).
Right-click the server instance and select Edit SQL Server Registration.
Select Subgroup of and select the parent group from the list.