function to render nested Twitter Bootstrap menu markup

pw_bootstrap_menu.php

<?php

/**
 *  render markup menu for bootstrap nested navigation
 *
 * @param  PageArray  $pa     pages of the top level items
 * @param  Page  $root   root page optional, if you use other root than home page (id:1)
 * @param  string  $output for returned string collection
 * @param  integer $level  internally used to count levels
 * @return string          menu html string
 */
function renderChildrenOf($pa, $root = null, $output = '', $level = 0) {
    if(!$root) $root = wire("pages")->get(1);
    $output = '';
    $level++;
    foreach($pa as $child) {
        $atoggle = '';
        $class = '';
        $has_children = count($child->children) ? true : false;

        if($has_children && $child !== $root) {
            if($level == 1){
                $class .= 'dropdown'; // first level boostrap dropdown li class
                $atoggle .= ' class="dropdown-toggle" data-toggle="dropdown"'; // first level anchor attributes
            } else {
                $class .= 'dropdown-submenu'; // sub level boostrap dropdown li class
            }
        }

        // make the current page and only its first level parent have an active class
        if($child === wire("page")){
            $class .= ' active';
        } else if($level == 1 && $child !== $root){
            if($child === wire("page")->rootParent || wire("page")->parents->has($child)){
                $class .= ' active';
            }
        }

        $class = strlen($class) ? " class='".trim($class)."'" : '';

        $output .= "<li$class><a href='$child->url'$atoggle>$child->title</a>";

        // If this child is itself a parent and not the root page, then render its children in their own menu too...
        if($has_children && $child !== $root) {
            $output .= renderChildrenOf($child->children, $root, $output, $level);
        }
        $output .= '</li>';
    }
    $outerclass = ($level == 1) ? "nav" : 'dropdown-menu';
    return "<ul class='$outerclass'>$output</ul>";
}

// bundle up the first level pages and prepend the root home page
$root = $pages->get(1);
$pa = $root->children;
$pa = $pa->prepend($root);

// Set the ball rolling...
echo renderChildrenOf($pa);


// example with pages further down in the tree

// $root = $pages->get("/about/");
// $pa = $root->children;
// $pa = $pa->prepend($root);

// add the root as the second parameter
// echo renderChildrenOf($pa,$root);