<?php
$arr = array(1,2,3,3,3,4,4,5,56,6,6,7,7,5,4,3,12,12,4,5,6,7,8,9,6,54,3,2,12,1,2,3,4,556,456,
1,2,3,3,3,4,4,5,56,6,6,7,7,5,4,3,12,12,4,5,6,7,8,9,6,54,3,2,12,1,2,3,4,556);
$cnt = count($arr);
$a = "";
$b = "";
?>
<select>
<option >Select</option>
<?php for($i=0;$i<floor($cnt/2);$i++) {
if((round($cnt/2) === 0) && (round($cnt/2)!==$i)){
//do nothing
}else{
$a .="<option>".$arr[$i]."</option>";
$b .="<option>".$arr[(($cnt/2))+$i]."</option>";
}
}
echo $a.$b;
?>
</select>