So you want something like:

use strict;
use warnings;
use XML::Twig;

my $FIELDS = {
    'AA' => {
        'Description' => '',
        'Type'        => 'Module',
        'File'        => 'Sample1.pl',
    },
    'BB' => {
        'Description' => 'Initiator',
        'Type'        => 'Methods',
        'File'        => 'Sample1.pl',
    },
    'CC' => {
        'Description' => 'Destructor',
        'Type'        => 'Methods',
        'File'        => 'Sample2.pl',
        'Values'      => {
            '1' => 'Ignore',
            '2' => 'Retry',
            '3' => 'Abort'
        }
    }
};

my $twig = XML::Twig->new (pretty_print => 'indented');

$twig->set_root (my $root = XML::Twig::Elt->new ('Fields'));
AddElements ($root, $FIELDS, 'Function');
$twig->print ();


sub AddElements {
    my ($parent, $hash, $type) = @_;

    for my $node (sort keys %$hash) {
        my $child;

        if ($type) {
            $child = $parent->insert_new_elt
                (last_child => $type, {'Name' => $node});
        } elsif ($node =~ /^[0-9]/) {
            $child = $parent->insert_new_elt
                (last_child => 'Value', {No => $node});
        } else {
            $child = $parent->insert_new_elt (last_child => $node);
        }

        if (! ref $hash->{$node}) {
            $child->set_text ($hash->{$node});
            next;
        }

        AddElements ($child, $hash->{$node});
    }
}
[download]

Prints:

<Fields>
  <Function Name="AA">
    <Description></Description>
    <File>Sample1.pl</File>
    <Type>Module</Type>
  </Function>
  <Function Name="BB">
    <Description>Initiator</Description>
    <File>Sample1.pl</File>
    <Type>Methods</Type>
  </Function>
  <Function Name="CC">
    <Description>Destructor</Description>
    <File>Sample2.pl</File>
    <Type>Methods</Type>
    <Values>
      <Value No="1">Ignore</Value>
      <Value No="2">Retry</Value>
      <Value No="3">Abort</Value>
    </Values>
  </Function>
</Fields>
[download]