I'm not sure what you are after, and I'm not the best at Tk menus. Maybe a cascade?

#!/usr/bin/perl
use warnings;
use strict;
use Tk;

my $top = MainWindow->new;

$top->geometry('100x100+100+100');

my $menu = $top->Menu( -type => 'menubar' );

$top->configure( -menu => $menu );

$menu->Cascade(
    -label     => '~Selections',
    -tearoff   => 1,
    -menuitems => [
        [
            Button => 'Level 1 choice 1',
            -command => [ \&printchoice, 'L1-C1' ]
        ],
        [
            Button => 'Level 1 choice 2',
            -command => [ \&printchoice, 'L1-C2' ]
        ],
        [
            Button => 'Level 1 choice 3',
            -command => [ \&printchoice, 'L1-C3' ]
        ],
        '',
        [
            Cascade    => 'Cascade 1',
            -tearoff   => 0,
            -menuitems => [
                [
                    Button => 'Cascade 1 Level 2 choice 1',
                    -command => [ \&printchoice, 'C1-L2-C1' ]
                ],
                [
                    Button => 'Cascade 1 Level 2 choice 2',
                    -command => [ \&printchoice, 'C1-L2-C2' ]
                ],
                [
                    Button => 'Cascade 1 Level 2 choice 3',
                    -command => [ \&printchoice, 'C1-L2-C3' ]
                ],
            ]
        ],
        [
            Cascade    => 'Cascade 2',
            -tearoff   => 0,
            -menuitems => [
                [
                    Button => 'Cascade 2 Level 2 choice 1',
                    -command => [ \&printchoice, 'C2-L2-C1' ]
                ],
                [
                    Button => 'Cascade 2 Level 2 choice 2',
                    -command => [ \&printchoice, 'C2-L2-C2' ]
                ],
                [
                    Cascade    => 'Cascade 3',
                    -tearoff   => 0,
                    -menuitems => [
                        [
                            Button => 'Cascade 3 Level 3 choice 1',
                            -command => [ \&printchoice, 'C3-L3-C1' ]
                        ],
                        [
                            Button => 'Cascade 3 Level 3 choice 2',
                            -command => [ \&printchoice, 'C3-L3-C2' ]
                        ],
                        [
                            Button => 'Cascade 3 Level 3 choice 3',
                            -command => [ \&printchoice, 'C3-L3-C3' ]
                        ],
                        [
                            Cascade    => 'Cascade 4',
                            -tearoff   => 0,
                            -menuitems => [
                                [
                                    Button => 'Cascade 4 Level 4 choic
+e 1',
                                    -command => [ \&printchoice, 'C4-L
+4-C1' ]
                                ],
                                [
                                    Button => 'Cascade 4 Level 4 choic
+e 2',
                                    -command => [ \&printchoice, 'C4-L
+4-C2' ]
                                ],
                                [
                                    Button => 'Cascade 4 Level 4 choic
+e 3',
                                    -command => [ \&printchoice, 'C4-L
+4-C3' ]
                                ],
                            ]
                        ]
                    ]
                ],
            ]
        ],
    ]
);

MainLoop;

sub printchoice {
    my $choice = shift;
    print $choice, "\n";
}
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