23      # of nodes in forest
1 0     1's parent is 0
2 1     2's parent is 1
3 1     3's parent is 1
4 1     4's parent is 1
5 2     5's parent is 2
7 3     etc., etc.
8 3
11 4
6 5
9 8
10 8
12 11
13 11
14 11
15 13
16 13
18 17
19 17
20 18
21 18
22 19