Thank you Jon,
Populate on demand works, however the treeview is acting different as before, but maybe I am just missing an other setting.
I want to show always all nodes that are direct children of the selected node, which is the default behaviour if PopuladeNodesFromClient is disabled. My tree has a max depth from 4. If I set the Expand Depth to 4, it works, but this loads the complete tree again.
The level is set to root.