You could do it this way (XML::Simple creates a hash of hashes because the nodes have an attribute called "name", I guess):

foreach $node ( keys( %{ $tree->{report}->{node} } ) ) {
  print "$node:values: $tree->{report}->{node}->{$node}->{values}\n";
}
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But you'd be better off adding KeyAttr to your new() call:

my $simple = XML::Simple -> new (KeyAttr => 'node');
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Because that way you will get an array of nodes

$tree = {
  'report' => {
    'ip' => '1.1.1.1',
    'id' => '0',
    'node' => [
      {
        'mid' => 'machine1',
        'time' => '110, 120, 130, 140, 150, 160',
        'name' => 'Winxp',
        'values' => '1, 2, 3, 4, 5, 6'
      },
      {
        'mid' => 'machine2',
        'time' => '110, 120, 130, 140, 150, 160',
        'name' => 'Win2003',
        'values' => '1, 2, 3, 4, 5, 6'
      }
    ]
  }
};
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Hint -- use Data::Dumper to look at the tree.