treeview - how to traverse a tree

Hi

I've created a treeview. The tree consists of a random number of parents, each with a number of children that can selected/deselected.

All items are selected by default. The idea is that the user deselects one or more items. 

I can detect in my call back whether something is selected / deselected. That works nicely.

When something is selected I can get the label of the item selected/deselect and the parent lg_hitem 

But how can I traverse through the complete list and figure out what items are selected and what items are deselected under each parent.

Thanks in advance.

Best regards

Ole