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

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

public Set 开发者_运维问答getSiblingNodes(Node node);

Should this method return a set including or excluding itself?

Thanks!

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

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.