==== PROBLEM ====
Code works on laptop with PHP 5

Not on server with PHP 4

My guess is there is a ByRef problem with the added items in 

_question_shake_tree()
= line =>    $root->children[$item->id] = $item;

==== CODE ====

function _question_tree_builder( $list, $root){
  $root->children=array();
print_r( array( 'initial root'=> $root));
  /* each item has a parent value */

  /*
   * try to add an item into the current tree
   * at least 1 item should succeed
   */
  $succes=true;
  while($succes){
    $succes= false;
    foreach( $list as $id => $item){
print_r(array( "root before shake"=> $root));
      if(_question_shake_tree( $root, $item)){
print_r(array( "root after shake"=> $root));
        $succes= true;
        break;
      }else{
print_r(array('unsuccesfull shake'=>array( 'root'=>$root,'item'=>$item)));
      }
    }
    if( $succes){
      unset($list[$id]);
    }
  }
}

function _question_shake_tree( &$root, &$item){
  if(($root->id== $item->parent)){
    // add all items to the children
    $root->children[$item->id] = $item;
print_r( array( 'Matching parent--child'=> array( 'root'=> $root, 'item'=>$item)));
    return TRUE;
  } else {
    if(isset($root->children)){
      foreach($root->children as $subtree){
        if( _question_shake_tree($subtree, $item)){
          return TRUE;
        }
      }
    } else {
//print_r( array( "FALSE with", 'root'=>$root, 'item'=>$item));
      return FALSE;
    }
  }
  return FALSE;
}


===== On server ====
// See http://questionary.build2be.com/?q=node/1/questions