Help with PHP Code

Shell Programming and Scripting
1 
<?php

chdir('/var/www/cacti/');   # Cacti's directory
include('./include/global.php');

duplicate_tree(ID_FROM, ID_TO);   # ID of tree

function duplicate_tree($tree_id_from, $tree_id_to) {

   $tree_items = db_fetch_assoc("SELECT * FROM graph_tree_items WHERE graph_tree_id = " . $tree_id_from);

   foreach ($tree_items as $item) {
      $item["id"] = "";
      $item["graph_tree_id"] = $tree_id_to;
      $new_item = implode("','", $item);
      $sql = "INSERT INTO graph_tree_items VALUES('" . $new_item . "')";
      db_execute($sql);
   }
}

?>

Can someone please help me make sense of the above code? it is meant to be used to create duplicate trees in cacti or moving existing trees into a new tree.

i have no idea what to give the script or how to run it. i ran it this way:

php duplicate_tree.php

and received an error:

PHP Notice:  Use of undefined constant ID_FROM - assumed 'ID_FROM' in /var/home/skysmart/duplicate_tree.php on line 6
PHP Notice:  Use of undefined constant ID_TO - assumed 'ID_TO' in /var/home/skysmart/duplicate_tree.php on line 6
PHP Warning:  Invalid argument supplied for foreach() in /var/home/skysmart/duplicate_tree.php on line 12