Item1 => {
	SubItem1 => {
		SubSubItem1 => 1,
		SubSubItem2 => 1,
		SubSubItem3 => 1,
	},
	SubItem2 => {
		SubSubItem1 => 1,
		SubSubItem2 => 1,
		SubSubItem3 => 1,
	},
},
Item2 => {
...

##</code><code>##

sub hashref_to_treeview {
	my $hashref = shift;
	my $treeview = shift; # Win32::GUI::Treeview object
	my $parent_node = shift || 0;
	
	return unless ref($hashref) eq 'HASH';
	
	for my $node ( sort keys %$hashref ) {
		my $new_node = $treeview->InsertItem(-text => $node, -parent => $parent_node);
		hashref_to_treeview($$hashref{$node}, $treeview, $new_node);
	}
}

##</code><code>##

my $id = 1;
my $data = {};
my $table1_results = $dbh->selectall_arrayref('SELECT field1 FROM table1 WHERE id = ?', {Slice => {}}, $id);
foreach my $field1 (@$table1_results) {
	$data->{$id}->{$table1_results->{field_of_interest}} = undef;
	my $table2_results = $dbh->selectall_arrayref('SELECT field2 FROM table2 WHERE field1 = ?', {Slice => {}}, $field1->{field1});
	foreach my $field2 (@$table2_results) {
		$data->{$id}->{$table1_results->{field_of_interest}}->{$table2_results->{field_of_interest}} = undef;
		...
	}
}

##</code><code>##

parent   child1   child2   child3
-------- -------- -------- --------
value1   value2   value3   value4
value1   value2a  value3   (null)
...


##</code><code>##

sub recursion_test {
	my $array = shift;
	
	my @results;
	while(@$array > 1){
		push @results, recursion_test($array);
	}
	return [$$array[0], undef];
}