To correctly display a taxonomy as a hierarchical facet you must configure the requisite Appkit service to retrieve the data structure that is configured in your Solr index. First you must create a service configuration: 
/conf
    /services
        /hierarchical
            /hierarchical.conf
The file ‘hierarchical.conf’ should be configured similar to this example: 
name: twigkit.search.solr.service.facet.GreedySolrHierarchicalFacetService
platform: platforms.solr
parents-suffix: _parent
platform
This specifies the configured platform where the taxonomy has been indexed. parents-suffix
The suffix that, if appended to the facet’s fieldname, designates the field containing parent node data. The suffix will depend on how the taxonomy data has been indexed. This service configuration is what is used when adding the hierarchical facet to your HTML page as in this example: 
<search:facet facet-name="location" show="6" show-more="100" max-characters="35" collapsible="true">
    <facet:hierarchical title="location" facet-name="location" platform="myHierarchicalPlatform" query="myHierarchicalQuery"></facet:hierarchical>
</search:facet>