code: public void addAttribute(TreeHtmlAttributeInfo attr)
      {
          if (_attribute == null) {
              _attribute = new ArrayList();
          }
          attr.setParent(this);
          _attribute.add(attr);
      }
docs: This method is called by the children tags of the TreeItem.  If there is a <code>TreeHtmlAttribute</code>
  it will set the attribute name and value.
  @param attr