QTreeWidgetItem* item = new QTreeWidgetItem(); item->setText(0, "Example Item"); item->setWhatsThis(0, "This is an example item that demonstrates the use of setWhatsThis.");In this example, a new QTreeWidgetItem is created and its text is set to "Example Item". The setWhatsThis function is then used to set the "What's This?" text of the first column to "This is an example item that demonstrates the use of setWhatsThis." The QTreeWidgetItem class is part of the Qt Core library, which is included in the Qt framework.