The {{ breadcrumb }} variable contains the breadcrumb for the page as an one dimensional array. The array contains item objects. You can loop over the breadcrumb and print the elements out like this:

<ul class="breadcrumb">
{% for element in breadcrumb %}
    <li><a href="{{ element.urlRel }}">{{ element.name }}</a></li>
{% endfor %}

All informations of the items are available, so check the chapter about the item variable for more details.