private void print(Node root){
        Node temp = root;
        do{
            System.out.println(temp.data);
            temp = temp.right;
        }while(temp != root);

        System.out.println();
        do{
            System.out.println(temp.data);
            temp = temp.left;
        }while(temp != root);
    }
http://cslibrary.stanford.edu/109/TreeListRecursion.html
Test cases
Null tree
src/com/interview/tree/BinaryTreeToCircularLinkList.java