I'm too lazy right now to do it with XML::Simple, but here's one I wrote a while ago to do it with XML::Parser. I wrote it to check that some XML I was writing was valid and wouldn't make the parser barf.

#!/usr/bin/perl
  
  use strict;
  use warnings;
  use XML::Parser;


$parser = new XML::Parser( Style => 'Tree' );
my $tree = $parser->parsefile( shift @ARGV );

use Data::Dumper;
print Dumper( $tree );
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ADDENDUM: I usually don't bother with putting a file open/write in something this short, I just use > filename.xml