Thanks for your suggestion! I tested it, and it works fine. :-)

Nevertheless, I solved the problem another way (as I don't like the idea of destroying my tree): I now additionally create the texts for the sub-elements, and then remove them from the top-element.

This solution also doesn't make me happy (it is somehow waste) - however I don't have any problems with runtime or memory-usage now, so it doesn't hurt. And the additional amount of electrons moving around heats up the air in the room - which is not to bad in winter ;-)

Rata