separate the construction of the model and the view
as expected, it is possible to change the model without destroying the tree-view widget
play around with tree iterators
code to go through the first branch of the tree
iteration through one branch and printing out values:
(("0:0" ("Klausf-Dieter Mustermann") (1351.0d0))
 ("0:1" ("Klausf-Dieter Musternn") (1351.0d0))
 ("0:2" ("Klausf-Dieter Musterman") (135.0d0))
 ("0:3" ("Ulrikef Langhals") (213.0d0)))