docs: public void addVerticesToSet(Set<VertexType> set) {
          // Add the vertex for this object
          set.add(this.m_vertex);
  
          // Add vertices for all children
          Iterator<SearchTree<VertexType>> i = childIterator();
          while (i.hasNext()) {
              SearchTree<VertexType> child = i.next();
              child.addVerticesToSet(set);
          }
      }