Gtk.ComboBox:row-span-column

"row-span-column"             Number                : Read / Write

If this is set to a non-negative value, it must be the index of a column of type %G_TYPE_INT in the model.

The values of that column are used to determine how many rows a value in the list will span. Therefore, the values in the model column pointed to by this property must be greater than zero and not larger than wrap-width.

Since 2.4