The Editable Tree Model example (https://doc.qt.io/qt-6/qtwidgets-itemviews-editabletreemodel-example.html) fails QAbstractItemModelTester "Common error test #3, the second column should NOT have the same children".
This can be easily solved in multiple ways, the fastest is to insert a check for the column being 0 in rowCount()

As a side note, that example also leaks the model. Another easy fix passing this as a 3rd argument to the constructor