You can build your menus in a custom way.

Sample Code:

<div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
    <ul class="nav navbar-nav">
        <% cama_menu_parse_items(current_site.nav_menus.find_by_slug('main_menu').children).each do |item| %>
            <% if item[:has_children] %>
                <li class="dropdown">
                    <a href="#" class="dropdown-toggle" data-toggle="dropdown"><%= item[:label] %> <b class="caret"></b></a>
                    <% if item[:levels] <= 1 %>
                        <ul class="dropdown-menu">
                            <% item[:children].each_with_index do |ss_item, index| %>
                                <li><a href="<%= ss_item[:url] %>"><%= ss_item[:label] %></a></li>
                            <% end %>
                        </ul>
                    <% else %>
                        <ul class="dropdown-menu multi-column columns-<%= (12/(12/item[:children].count).ceil).ceil %>">
                            <div class="row">
                                <% item[:children].each do |sub_item| %>
                                    <div class="col-md-<%= (12/item[:children].count).ceil %>">
                                        <ul class="multi-column-dropdown">
                                            <% ((sub_item[:children] || []) << sub_item).each_with_index do |ss_item, index| %>
                                                <% if index > 0 %>
                                                    <li><a href="<%= ss_item[:url] %>"><%= ss_item[:label] %></a></li>
                                                <% else %>
                                                    <h6><%= ss_item[:label] %></h6>
                                                <% end %>
                                             <% end %>
                                        </ul>
                                    </div>
                                <% end %>
                                <div class="clearfix"></div>
                            </div>
                        </ul>
                    <% end %>
                </li>
            <% else %>
                <li><a href="<%= item[:url] %>"><%= item[:label] %></a></li>
            <% end %>
        <% end %>
    </ul>
</div>

Result:

Sample Source:
https://codepen.io/dustlilac/pen/Qwpxbp