QTreeView里的QStandardItemModel添加了QStandardItem，QStandardItem下面有子QStandardItem，如果添加后让QTreeView自动展开该节点呢？
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void QTreeView::expandAll () [slot]
Expands all expandable items.
Warning: if the model contains a large number of items, this function will take some time to execute.
This function was introduced in Qt 4.2.