Help with printing hierarchical data

[torrent]

Hi,

I wish to able to produce a list of links, like this:
link1/
link1/link2/
link1/link2/link3
link1/link2/link3/link4/
link1/link2/link3/link4/link4a
link1/link2/link3/link4/link5
I am using a Modified Preorder Tree Traversal algorithm to produce the hierachical structure.
The database table looks like this:

+-------------------+
| lft | name  | rgt |
+-------------------+
|  1  | link1 |  16 |
+-------------------+
|  2  | link2 |  15 |
+-------------------+
|  3  | link3 |  14 |
+-------------------+
|  4  | link4 |  13 |
+-------------------+
|  5  | link4a|  6  |
+-------------------+
|  7  | link4b| 10  |
+-------------------+
|  8  | link5 |  9  |
+-------------------+
|  11 | link4c| 12  |
+-------------------+

I have produced a class which does everything I need, such as determine parent<-->children relationships,
insert new nodes, etc. The bit I am struggling with is printing the information in the format I showed up top.
I want to "walk" down the tree and produce the link list as shown. I just don't seem to be able to get it right.
I have been able to produce an indented link list:

link1
	link2
		link3
			link4
				link4a
				link4b
				link4c
				link5

The method where all this takes place in displayTree().
Any help most appreciated!
Thanks
Code follows:

<?php
  include('DB.php');
  class tree
  {
      var $newName;
      function tree($parent) 
      {
          $dbh = new DB();
          $dbh->connect();
          $this->_parent = $parent;
          $qry = "SELECT lft, name, rgt FROM subcategory1 WHERE name = '$this->_parent'";
          
          $dbh->execute($qry);
          $this->_parentValues = $dbh->fetch_assoc();   
      }      
      function getChildren()
      {
          $dbh = new DB();
          $dbh->connect();
          $qry  = "SELECT * ";
          $qry .= "FROM subcategory1 ";
          $qry .= sprintf("WHERE lft BETWEEN %s AND %s ", $this->_parentValues['lft'], $this->_parentValues['rgt']);
          $qry .= "ORDER BY lft";  
          
          $dbh->execute($qry);
          return $dbh->fetch_all_assoc();       
      }
      function addChild($name)
      {
          $dbh = new DB();
          $dbh->connect();
          $this->newNode = $name;          
          $this->_updExistingValues();   
          $qry['new'] = sprintf("INSERT INTO subcategory1 VALUES (%s, '%s', %s)", $this->_parentValues['lft'] + 1, $this->newNode, $this->_parentValues['lft'] + 2);            
          $dbh->execute($qry['new']);     
          return;
      }
      function displayTree($branch) 
      {
          $_stack = array();
          foreach($branch as $row) {
              if (count($_stack) > 0) {
                 while($_stack[count($_stack) - 1] < $row['rgt']) {
                     array_pop($_stack);
                 }
              }
              //print str_repeat('    ', count($_stack)) . $row['name'] . "\n";
              $_stack[] = $row['rgt'];
          }
      }      
      function _updExistingValues()
      {
          $dbh = new DB();
          $dbh->connect();
          $qry['rgt'] = "UPDATE subcategory1 SET rgt = rgt + 2 WHERE rgt > {$this->_parentValues['lft']}";
          $qry['lft'] = "UPDATE subcategory1 SET lft = lft + 2 WHERE lft > {$this->_parentValues['lft']}";
          $dbh->execute($qry['rgt']);
          $dbh->execute($qry['lft']);     
          return;          
      }
  }
 
  $myTree = new tree('link1');
  $branch = $myTree->getChildren();
  $myTree->displayTree($branch);
  
/*
  $myTree->addChild('link4c');
  print_r($myTree->getChildren());
*/
?>