Levels aren't numbered, so it's easy to lose track of which level you're on. I've added what each looks like after this section.

Level select unlocks after clearing all 55 levels, in case you need to go back and optimise a level.

1: ►
2: ►　▲
3: ▲　►　◄　▲
4: ►　►　▼　▲　▲
5: ▼　◄　▲　▲　►　►　▼　▼

6: ►
7: ▼
8: ▲　►
9: ▼　◄　◄
10: ▲　▼　►　▲

11: ▲　▲　◄　◄
12: ►　▼　◄　◄
13: ▲　▲　▼　►
14: ▼　◄　▼　▲　►　►
15: ▲　►　▼

16: ►　▲　◄　◄　◄　▼
17: ▼　◄　▲　◄
18: ▲　▼　▼　▲　►
19: ▲　►　▼　◄　◄　▲　►　▲
20: ▲　►　►　▼

21: ▲　►
22: ▼　▼　►　▼　►　►　▲　▲　◄　▲
23: ▲　◄　◄　▼
24: ▼　◄　▼　◄
25: ◄　►　►　◄　▲　▲

26: ►　▲　▼　◄　◄　▲
27: ◄　▲　►
28: ◄　▼　►　►　▼　◄
29: ◄　◄　▼　▼　►　►　▲　◄
30: ◄　►　▲　◄

31: ►　▲　◄
32: ▲　►　▲　▼　▼　▼　◄　►　▼　▲　▲　►
33: ►
34: ◄　▼　►
35: ◄　▼　▲　▲

36: ◄　►　▲　◄
37: ▲　►　▼
38: ►　◄　▼　▲　◄　►　▲
39: ▼　◄　▲　▼　►　▼　◄　►　►　▲
40: ▲　▼　▼　►　▲　▼　▼　◄

41: ►
42: ►　◄　▼
43: ◄　▲　►　▼　◄
44: ▲　▼　►　►　►　▲　▼　◄　◄　▲　▲　◄　◄
45: ▼　▲　◄

46: ▲　▼　►　►　▲　◄　◄　▼　►
47: ►　◄　▼　►　▲　▼　►　▲　◄　▼　▲　◄
48: ►
49: ►　▲　►
50: ▲　▼　◄　►　►　◄　▼　►　▲　◄　▼

51: ▲　►　▼　◄　▼　►　▲　◄　▲
52: ▼　►　▲　▲
53: ▼　▼　►　►　►　►　▲　▲
54: ▲　►　▼
55: ▲　►　►　►　►　►　►　►　►　►　►　▼

I didn't want to dump 55 images into the guide and make it unnecessarily long, so I've grouped them into images of ten. Click on each to zoom in.