In a tree data structure, is a node a sibling of itself?

Question

I am building a tree like data structure. What is the expected behavior if I have a method

public Set getSiblingNodes(Node node);

Should this method return a set including or excluding itself?

Thanks!

Answer 1

No. It should contain only it's siblings.
A node is not a sibling of itself.
(Why would you think otherwise?)

Answer 2

generally no, But you can define some sort of tree, where siblings build the circular list and then if this list has one node it will be a sibling of itself.