Perfectly balanced tree

gistfile1.php

function tree(&$tree, $num_nodes)
{
  if($num_nodes == 0)
    return null;
 
  $left = (int)($num_nodes / 2);
  $right = $num_nodes - $left -1;
 
  $tree[]['value'] = (int)(mt_rand( 1, 50) / $num_nodes+1);
  $last = count($tree)-1;
 
  $tree[$last]['left'] = tree($tree, $left);
  $tree[$last]['right'] = tree($tree, $right);
 
  return $last;
}