_includes/header.html

<nav class="navbar navbar-default navbar-fixed-top" role="navigation">
    <div class="container">
        <div class="navbar-header">
            <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#main-menu" aria-expanded="false">
                <span class="sr-only">Toggle navigation</span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </button>
            <a href="{{site.path.website | relative_url}}/" class="navbar-brand">
                <img src="{{site.path.style | relative_url}}/img/apache-brooklyn-logo-244px-wide.png" alt="Apache Brooklyn" />
            </a>
        </div>
        <div class="collapse navbar-collapse" id="main-menu">
            <ul class="nav navbar-nav navbar-right">
                {% for item in site.data.menu %}
                <li class="dropdown{% if page.breadcrumb_paths contains item.path %} active{% endif %}">
                    {% if item.menu_customization.type == "button" %}
                    <a href="{{item.url}}" class="btn btn-default navbar-btn">{{ item.title_in_menu | downcase }}</a>
                    {% else %}
                    <a href="{{item.url}}" data-toggle="dropdown">{{ item.title_in_menu | downcase }} {% if item.menu %}<span class="caret"></span>{% endif %}</a>
                    {% if item.menu %}
                    <ul class="dropdown-menu" role="menu">
                        <li>
                            <a href="{{item.url}}">{{item.title_in_menu}}</a>
                        </li>
                        <li class="divider"></li>
                        {% for item2 in item.menu %}
                        {% if item2.menu_customization.dropdown_new_section %}<li class="divider"></li>{% endif %}
                        <li {% if item2.menu_customization.dropdown_section_header %}class="section"{% endif %}>
                            <a href="{{item2.url | relative_url}}">{{item2.title_in_menu}}
                                {% if item2.external %}&nbsp;<span class="octicon octicon-link-external"></span>{% endif %}</a>
                        </li>
                        {% if item2.menu_customization.dropdown_section_header %}<li class="divider"></li>{% endif %}
                        {% endfor %}
                    </ul>
                    {% endif %}
                    {% endif %}
                </li>
                {% endfor %}
            </ul>
        </div>
    </div>
</nav>