Adding a right-click menu for specific items in QTreeView

I would do this in the following way:

Configure the context menu

ui->treeView->setContextMenuPolicy(Qt::CustomContextMenu);
connect(ui->treeView, SIGNAL(customContextMenuRequested(const QPoint &)), this, SLOT(onCustomContextMenu(const QPoint &)));

Implement the context menu handling

void MainWindow::onCustomContextMenu(const QPoint &point)
{
    QModelIndex index = ui->treeView->indexAt(point);
    if (index.isValid() && index.row() % 2 == 0) {
        contextMenu->exec(ui->treeView->viewport()->mapToGlobal(point));
    }    
}