TOPIC: L5.04 Create WBS - Question about determining levels of componets

The "Sample Exam Question" at the end of this lesson request you to "identify the correct code of accounts for a WBS component at the 3rd level" and indicates that the correct answer is "2.3.2". However, earlier in the lesson, around 10:10 of the video where the WBS Table sample is shown, there is an initial level of "O" with the highest level deliverable. Why is this initial level of 0 not taken into consideration when determining the WBS component at the 3rd level? I would have thought the answer to be something like 1.1. since it's 3rd in the list of the Code of Accounts/WBS Components. If that initial line of 0 is not considered a level, what is it called?

0
1
1.1
1.2