You should notice that once 3A is completed at 0:06, the song repeats itself for the next six seconds. The whole 12-second intro is just 3A played twice, and we'll call it 4A. It's at this point that the hierarchy starts to break down, because there's no variation between the 3As, meaning 4A is also not noticeably varied from them. This expressed in the graph by 4A being the same color as 3A, brown, despite being in the same idea chain. The longer you play the same thing repeatedly, the more you risk boring the listener, though you may find a reason to do so. In this particular case, it does get away with it, because it's the opening of the song and is trying to set the tone, and it's both fast and still varied enough up to Level 3 that it doesn't get annoying within the short 6 seconds in which it does so. If it was just 1A played for all 12 seconds, it would be unacceptable.
Now take a look at the next part, which starts at 0:12. This segment has its own 1A, 1B, 2A, etc, that are all different and unrelated to the last segment's set. However, this segment is different in that it does not repeat its 3A, and this happens because of a single change in Level 1. At the end of the segment, instead of a second playing of 1C, it introduces another new idea, 1D. This has a trickle-up effect on variation, because it also means that, instead of there being a second playing of 2B like in the first segment, there's now a new idea in its place called 2C, which in turn also means that there is not a second 3A, but a new idea called 3B. This small change makes its structure significantly more varied than the intro. This whole segment is called 4B.
See Pic 3. This is the same graph, zoomed out. It shows that the song actually has two additional Levels, and that the song has two more Level 4 segments, for a total of four. They last almost as long as A and B, but for brevity's sake, I didn't expand it to their full size, or mark out the exact times of their component ideas, only the time span in which they occur. Their structure is identical to 4B's. 4C is what could be considered the bridge of the song. It sounds very different from the rest of it, but still conforms to the same structure.
4D is the finale, so rather than doing its own thing like 4C, it instead uses the opportunity to tie together the structure of the entire song. 4D is actually based around the same 1A from back in 4B, which makes them related. Prior to this, 4A and 4B had no direct relationship aside from being adjacent and having a similar rhythm. However, now there are two sets of coupled Level 4 segments where the final segment is based on 4B's 1A. Until this point, it was always the final item in any coupling that would be the variation, but the inverse is also acceptable. 4C's seemingly non-sequitur uniqueness was acually the variation in the 4C and 4D coupling. We'll call the first of these new sets 5A, and the second 5B. In this way, 4B's 1A acts as a cornerstone that ties the whole song together. Now, we know that 5A and 5B are related, and the song is all one completed concept on its own Level, as 6A.
You see the patterns you see in pop music, such as the common placement orders of verses, choruses, and bridges, because they follow this concept. I don't know how strictly songs have to adhere to this concept, but it's definitely the norm to do so in non-experimental music, and I've never encountered a song that's worse off for doing it. That's the basic idea, so I'm cutting it here. I didn't expect this to turn into an autistic essay so fast.