Parent/child tree generator

<?php

$nav_query = mysql_query("SELECT * FROM `cm2year` ORDER BY `catid`");
$tree = "";     // Clear the directory tree
$depth = 1;     // Child level depth.
$top_level_on = 1;   // What top-level category are we on?
$exclude = array();   // Define the exclusion array
array_push($exclude, 0); // Put a starting value in it
 
while ( $nav_row = mysql_fetch_array($nav_query) )
{
 $goOn = 1;   // Resets variable to allow us to continue building out the tree.
 for($x = 0; $x < count($exclude); $x++ )  // Check to see if the new item has been used
 {
  if ( $exclude[$x] == $nav_row['catid'] )
  {
   $goOn = 0;
   break;    // Stop looking b/c we already found that it's in the exclusion list and we can't continue to process this node
  }
 }
 if ( $goOn == 1 )
 {
  $tree .= "Year". $nav_row['catname'] . "<br>";    // Process the main tree node
  array_push($exclude, $nav_row['catid']);  // Add to the exclusion list
  if ( $nav_row['category_id'] < 6 )
  { $top_level_on = $nav_row['catid']; }
 
  $tree .= build_child($nav_row['catid']);  // Start the recursive function of building the child tree
 }
}
 
function build_child($oldID)   // Recursive function to get all of the children...unlimited depth
{
 global $exclude, $depth;   // Refer to the global array defined at the top of this script
 $child_query = mysql_query("SELECT * FROM `cm3model` WHERE parentid=" . $oldID);
 while ( $child = mysql_fetch_array($child_query) )
 {
  if ( $child['catid'] != $child['parentid'] )
  {
   for ( $c=0;$c<$depth;$c++ )   // Indent over so that there is distinction between levels
   { $tempTree .= "&nbsp;"; }
   $tempTree .= "options[" . $child['parentid'] ."]". "=new Option" . "(\"" . $child['catname'] ."\"" . "," . "\"http://www.intimegraphics.com/category_s/" . $child['catid']. ".htm\")<br>";
   $depth++;  // Incriment depth b/c we're building this child's child tree  (complicated yet???)
   $tempTree .= build_child($child['catid']);  // Add to the temporary local tree
   $depth--;  // Decrement depth b/c we're done building the child's child tree.
   array_push($exclude, $child['catid']);   // Add the item to the exclusion list
  }
 }
 
 return $tempTree;  // Return the entire child tree
}
 
echo $tree;
 
?>