Convert a tree into a liked list where nodes in the linked list represent level order traversal.

Now a simpler one:
For ex. if tree is
.............|1|..............
............./..\..............
.........|2|.... |3|..........
....... / \...... / \..........
.... |4|..|5| ..|6|...|7|....

Make a list like 1-->2-->3-->4-->5-->6-->7.