Remove a given items and its siblings from their parent
void PtGenTreeRemoveList( PtWidget_t *tree, PtGenTreeItem_t *first );
This function unlinks the item first and its siblings (together with their children) from their parent (and previous sibling) and sets their parent fields to NULL. The tree argument must point to the widget that contains the items or can be NULL if the items don't belong to any tree.
If tree is NULL and first has no parent but has a previous sibling, PtGenTreeRemoveList() can't find the previous sibling and can't unlink first from its previous sibling.