docs: protected void executeOpen(boolean fireEvents) {
  
          m_styleVar.setValue(m_open ? CSS.listTreeItemOpen() : CSS.listTreeItemClosed());
          setLeafStyle(false);
          m_children.getElement().getStyle().clearDisplay();
          if (m_opener.isDown() != m_open) {
              m_opener.setDown(m_open);
          }
          if (fireEvents) {
              if (m_open) {
                  fireOpen();
              } else {
                  fireClose();
              }
          }
          // reset the leaf style according to the child count
          setLeafStyle(0 == getChildCount());
      }