code: public void setLeafStyle(boolean isLeaf) {
  
          if (isLeaf) {
              m_leafStyleVar.setValue(CSS.listTreeItemLeaf());
          } else {
              m_leafStyleVar.setValue(CSS.listTreeItemInternal());
          }
      }
docs: Sets the tree item style to leaf, hiding the list opener.<p>
  
  @param isLeaf <code>true</code> to set to leaf style