use strict;
use warnings;
use Tk;
use Tk::Tree;

my $fgcolor = "#000000";                   # foreground color
my $bgcolor = "#FFFFFF";                   # background color
my $list_highlight_color = "#0099FF";      # list highlight color
my $text_font = 'helvetica 12';            # Body text font
my $title_font = 'helvetica 12 bold';      # Title text font

my $mw = MainWindow->new();

$mw->optionAdd("*background", $bgcolor);
$mw->optionAdd("*foreground", $fgcolor);
$mw->optionAdd("*rotext*font", $text_font);
$mw->optionAdd("*tree*font", $text_font);
$mw->optionAdd("*entry*font", $text_font);

my $tree;
$tree = $mw->Scrolled('Tree', -font=>$text_font, -scrollbars=>'ose', -selectmode=>'extended', -selectbackground=>$list_highlight_color, -highlightcolor=>$bgcolor, -drawbranch=>0, -browsecmd=>sub {
            foreach ($tree->selectionGet) {
                unless (/\./) {  # do not allow selection of top level items
                    $tree->selectionClear($_);
                }
            }
})->pack(-side=>'top', -fill=>'both', -expand=>1);

for my $top ( 1 .. 3) {
    $tree->add( $top, -text => $top );
    for ( 'A' .. 'C') {
        $tree->add( "$top.$_", -text => "$_" );
    }
}

MainLoop();