Sets whether same node can exist in the tree at the same level
if the value of the property true
this method doesn't allow to add/insert two same node
at the same level for the particular parent.
Sets the child parent relationship to true or false
this property is used when the tree is checkbox
and one can want to makes the all the child checked
on checked the parent of those child
and from all the checked childs if one child is unchecked
the parent will also unchecked