getting data out of the simple tree model example

[qt_gotcha]

Fooling around with the treemodel, I hoped this would work. I want to wrte the contents of the treemodel in the simpletreemodel example to a text file. I thought the index function would get the correct data from the child items if the column counter > 0, so that the contents of the children are simply accessible with model.data(i,j). All I get is a list of contents of the parent items (so at index i,0) , I cannot acces the content of the children.

QFile fout("some.txt");
    fout.open(QIODevice::ReadWrite);
    for (int i = 0; i < model.rowCount(); i++)
    {
        QString S = "";
        for (int j = 0; j  < model.columnCount(); j++)
        {
	QVariant d = model.data(model.index(i,j),0);
	S = S + d.toString()+";";
         }
         S = S + "\n";
        QByteArray line(S.toAscii());
         fout.write(line);
    }
    fout.close();

QFile fout("some.txt");
    fout.open(QIODevice::ReadWrite);
    for (int i = 0; i < model.rowCount(); i++)
    {
        QString S = "";
        for (int j = 0; j  < model.columnCount(); j++)
        {
	QVariant d = model.data(model.index(i,j),0);
	S = S + d.toString()+";";
         }
         S = S + "\n";
        QByteArray line(S.toAscii());
         fout.write(line);
    }
    fout.close();

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my reasoning is not correct obviously, but I don't get it. Thanks