QTreeWidgetItem and background color

[swiety]

How can i change the background color of a qtreewidgetitem?
When item has a parent, and e.g 3 columns then

QBrush b( Qt::red );
item->setBackground( 0, b );
item->setBackground( 1, b );
item->setBackground( 2, b );

QBrush b( Qt::red );
item->setBackground( 0, b );
item->setBackground( 1, b );
item->setBackground( 2, b );

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doesn't work because first column( 0 ) isn't a really first column, and i have this: