$ sudo apt-get update
$ sudo apt-get install classicmenu-indicator 

classicmenu-indicator is installed in your system.

Make ensure the classicmenu-indicator package were installed using the commands given below,

$ sudo dpkg-query -l | grep classicmenu-indicator *

You will get with classicmenu-indicator package name, version, architecture and description in a table

classicmenu-indicator package basic information: