sub find
{
  my $tree = shift;
  my $node_value=shift;
  my $last=0;
  my $child;
  my $func;
  $func = sub ($)
  {
    $child=shift();
    $last=1 if($child->getNodeValue() eq $node_value);
    my @children=$child->getAllChildren();
    $func->(shift(@children)) while(@children && !$last);
  };
  $func->($tree);
  return $child if($last);
  return undef;
}