<?php
header('Content-type: application/xml; charset="utf-8"');

$owoce = array('jabłko', 'gruszka', 'banan', ...);

echo '<?xml version="1.0" encoding="utf-8"?>';
echo '<owoce>';

foreach ($owoce as $owoc) {
    echo '<owoc>';
    echo $owoc;
    echo '</owoc>';    
}

echo '</owoce>';

?>