use Tk;
$mw = new MainWindow;
$menu = $mw->Menu
    (-menuitems =>
     [
      [Cascade => "~Menu", -menuitems =>
       [
        [Cascade => "~Cascade", -menuitems =>
         [
          [Button => "~Command in Cascade", -command => sub { } ],
         ]
        ]
       ]
      ]
     ]
    );
$mw->configure(-menu => $menu);