Let's take the following graph as an example:
-------------
- G-H-I-J
- / \
+ G-H-I-J
+ / \
A-B-C-D-E-F O
- \ /
- K-L-M-N
+ \ /
+ K-L-M-N
-------------
If we compute the following non optimal function on it:
we get:
-------------
- 4 3 2 1
- G-H-I-J
+ 4 3 2 1
+ G-H-I-J
1 2 3 4 5 6/ \0
A-B-C-D-E-F O
- \ /
- K-L-M-N
- 4 3 2 1
+ \ /
+ K-L-M-N
+ 4 3 2 1
-------------
but with the algorithm used by git bisect we get:
-------------
- 7 7 6 5
- G-H-I-J
+ 7 7 6 5
+ G-H-I-J
1 2 3 4 5 6/ \0
A-B-C-D-E-F O
- \ /
- K-L-M-N
- 7 7 6 5
+ \ /
+ K-L-M-N
+ 7 7 6 5
-------------
So we chose G, H, K or L as the best bisection point, which is better
-------------
A-B-C-D-E-F-G <--main
\
- H-I-J <--dev
+ H-I-J <--dev
-------------
The commit "D" is called a "merge base" for branch "main" and "dev"