flowchart TB
c1-->a2
subgraph one
a1-->a2
end
subgraph two
b1-->b2
end
subgraph three
c1-->c2
end
one --> two
three --> two
two --> c2
https://juejin.cn/post/7053730154710827045#heading-10 https://juejin.cn/post/6844904037377114119