When i click on parent, it just shows the child under it and so on (which can also be expanded further with initial arrow as marked in Red in the below screen-shot
it looks like your parent node has been deleted/moved without affect children marked. Xwiki offers a dummy node to allow you to still access the children although the path to them is broken. So you either need to create a new parent, restore the old one or move your children pages to the new parent location. Then the current dummy parent page will vanish from the navigation tree.