Thank you for your answer, it solved the issue.
I got one more question with TreeView. I do change autoCheck while being in action. And the problem is that if selected parent has no selected childs it will get unchecked.
Query 1: How do I maintain same selectedNodes before autoCheck and after autoCheck. For example if I still want parent to maintain selected and be in selectedNodes even if it has no selected child
Query 2: Can I somehow get rid of "mixed" status and leave just checked and unchecked
In example we got 2 parents selected, one parent has selected child another one doesn't.
This is what happens when I apply this.treeView.autoCheck = true. Parent that had selected child gets "mixed" status, but the one that didn't selected child gets unselected. And now selectedNodes before autoCheck and after autoCheck are different, but I only changed the property.