Treeview with checkbox

I have filtered Dhtmlx treeview (with checkbox) in client side and now the filtered items are visible. For Ex: I have 100 items (node) in treeview, after filtered we have only 15 items are visible. Question: Now i have to selectAll / UnselectAll for the visible 15 items only. How to iterate dhtmlx visible treeview?

Unfortunately there is no method allowing to iterate the tree items.
Could you please, clarify your using filtering logic.