To add a track to a character, group, or subcharacter
A black line appears above or below the selected clip’s track. This line indicates that Maya will insert a single track above or below the selected clip’s track when you release the mouse button.
 -click a track, and select one of the following options from the menu that appears: Insert Track Above or Insert Track Below.
-click a track, and select one of the following options from the menu that appears: Insert Track Above or Insert Track Below. 
                  These options insert a track above or below the selected clip’s track. See Context-sensitive menu.