//如果不想要展开折叠图标（三角图标），可以用以下代码
{
//隐藏根节点项前的图标（展开折叠图标）
ui.treeWidget->setRootIsDecorated(false);
//如果只是隐藏根点的展开折叠图标而子节点保留，则只需要上面语句
ui.treeWidget->setStyleSheet("QTreeView::branch:has-children:!has-siblings:closed,\
QTreeView::branch:closed:has-children:has-siblings{border-image: none; image: none;}\
QTreeView::branch:open:has-children:!has-siblings,\
QTreeView::branch:open:has-children:has-siblings{border-image: none; image: none;}");
}
//如果想把展开折叠图标（三角图标）换成自己的图标，可以用以下代码
{
ui.treeWidget->setStyleSheet("QTreeView::branch:has-children:!has-siblings:closed,\
QTreeView::branch:closed:has-children:has-siblings{border-image: none; image: url(:/QtXmlTest/Resources/image/plus.png);}\
QTreeView::branch:open:has-children:!has-siblings,\
QTreeView::branch:open:has-children:has-siblings{border-image: none; image: url(:/QtXmlTest/Resources/image/minus.png);}");
}
//把plus.png和minus.png改为自己的图片就可以了
一份完整的QTreeWidget示例，下载地址：http://download.csdn.net/download/jxbinwd/10044343