PHP Balanced tree - Add element/node

This script add element to the tree if it doesn't exist, if exists just increment it counter.

function search_btree( $value, $ptr, $higher, $ptr0 = 0,$node = 'left' )
{
 global $tree;
 static 
  $first_run = 1,
  $higher,
  $beginning;  
 
 if( !$tree[$ptr]['value'] )// insertion
 {
  if( !$first_run )// create new element in the tree array - $tree
  {
   $tree[] = array();
   $ptr = count($tree)-1;
    
   $tree[$ptr0][$node] = $ptr;// put current node in parent's left or right node

  }else{// $tree[0] is already create so we just use is
   $first_run--;
   $beginning = $ptr;
  }
  $higher = true;
  
  $tree[$ptr]['value'] = $value;
  $tree[$ptr]['left'] = null;
  $tree[$ptr]['right'] = null;
  $tree[$ptr]['bal'] = 0;
  $tree[$ptr]['count'] = 1;
  
 }
 else
 {
  if( $value < $tree[$ptr]['value'] )
  {
   search_btree( $value, $tree[$ptr]['left'], $higher, $ptr );
   if( $higher )
   {
    switch( $tree[$ptr]['bal'] )
    {
     case 1:
      $tree[$ptr]['bal'] = 0;
      $higher = false;
     break;
     case 0:
      $tree[$ptr]['bal'] = -1;
     break;
     case -1:
      $ptr1 = $tree[$ptr]['left'];
      if( $tree[$ptr1]['bal'] == -1) // individualli flip LL
      {
       
       $tree[$ptr]['left'] = $tree[$ptr1]['right'];
       $tree[$ptr1]['right'] = $ptr;
       $tree[$ptr]['bal'] = 0;


       if( $ptr == $beginning )
        $beginning = $ptr1;
       // replaces $ptr with $ptr1 in parent left or right node
       replace_pointer_link( $ptr, $ptr1 );
       $ptr = $ptr1;
      }
      else
      {
       $ptr2 = $tree[$ptr1]['right'];

       $tree[$ptr1]['right'] = $tree[$ptr2]['left'];
       $tree[$ptr2]['left'] = $ptr1;
       
       $tree[$ptr]['left'] = $tree[$ptr2]['right'];
       $tree[$ptr2]['right'] = $ptr;
       
       if( $tree[$ptr2]['bal'] == -1 )
        $tree[$ptr]['bal'] = 1;
       else
        $tree[$ptr]['bal'] = 0;
        
       if( $tree[$ptr2]['bal'] == 1 )
        $tree[$ptr1]['bal'] = -1;
       else
        $tree[$ptr1]['bal'] = 0;
       
       if( $ptr == $beginning )
        $beginning = $ptr2;
       replace_pointer_link( $ptr, $ptr2 );
       $ptr = $ptr2;
       
      }
      $tree[$ptr]['bal'] = 0;
      $higher = false;
     break;
    }
   }
  }
  else if( $value > $tree[$ptr]['value'] )
  {
   search_btree( $value, $tree[$ptr]['right'], $higher, $ptr, 'right' );
   if( $higher )
   {
    switch( $tree[$ptr]['bal'] )
    {
     case -1:
      $tree[$ptr]['bal'] = 0;
      $higher = false;
     break;
     case 0:
      $tree[$ptr]['bal'] = 1;
     break;
     case 1:
      $ptr1 = $tree[$ptr]['right'];
      if( $tree[$ptr1]['bal'] == 1 )// individualli flip RR
      {

       $tree[$ptr]['right'] = $tree[$ptr1]['left'];
       $tree[$ptr1]['left'] = $ptr;
       
       $tree[$ptr]['bal'] = 0;
       
       if( $ptr == $beginning )
        $beginning = $ptr1;
       replace_pointer_link( $ptr, $ptr1 );
       $ptr = $ptr1;
      }
      else//RL
      {
       
       $ptr2 = $tree[$ptr1]['left'];
       
       $tree[$ptr1]['left'] = $tree[$ptr2]['right'];
       $tree[$ptr2]['right'] = $ptr1;
       
       $tree[$ptr]['right'] = $tree[$ptr2]['left'];
       $tree[$ptr2]['left'] = $ptr;
       
       if( $tree[$ptr2]['bal'] == 1 )
        $tree[$ptr]['bal'] = -1;
       else
        $tree[$ptr]['bal'] = 0;
       
       if( $tree[$ptr2]['bal'] == -1 )
        $tree[$ptr1]['bal'] = 1;
       else
        $tree[$ptr1]['bal'] = 0;
       
       if( $ptr == $beginning )
        $beginning = $ptr2;

       replace_pointer_link( $ptr, $ptr2 );
       $ptr = $ptr2;
      }
      $tree[$ptr]['bal'] = 0;
      $higher = false;
     break;
    }
   }
  }
  else
  {
   $tree[$ptr]['count']++;
   $higher = false;
  }
 }
 return $beginning;
}
//replaces $old_ptr with $new_ptr in the parent node's left or right node
function replace_pointer_link( $old_ptr, $new_ptr )
{
 global $tree;

 for( $i=0; $i < count($tree); $i++)
 {
  if( $i === $new_ptr )
   continue;//prevents replacing $old_ptr with $new_ptr in $tree[$new_ptr] 
 
  // if $tree[$i]['left'] is empty and we are checking for link to node 0($old_ptr=0),
  // ('' == 0)==true, but ('' === 0)==false
  // we don't need to put link to node 0 on empty nodes
  if( $tree[$i]['left'] === $old_ptr ){
   $tree[$i]['left'] = $new_ptr;
   return;
   }
   elseif( $tree[$i]['right'] === $old_ptr)
  {
   $tree[$i]['right'] = $new_ptr;
   return;
  }
 }

}
//
// Example:
//

$my_tree = array();
// you could create as many trees as you want
// but when you want to work with them use $tree = &$my_tree;
$tree = &$my_tree;
$start = 0;

// test all 4 cases of rebalancing when
// adding element in balanced tree
$values = array( 4, 5, 7, 2, 1, 3, 6);
foreach( $values as $val )
{
 $start = search_btree( $val, $start, false);
}
echo "<html><body>";
echo "start=$start;";
echo "<pre>";
print_r( $my_tree );
echo "</pre>";
echo "<br><br>";
echo "</body></html>";

?>

Source