Hey, I was looking for the same thing so I created my own version of a PERT/Network/Graph diagram if anyone is still looking for similar solution, code below image.

@startuml PERT
left to right direction
' Horizontal lines: -->, <--, <-->
' Vertical lines: ->, <-, <->
title PERT: Project Name
map Kick.Off {
}
map task.1 {
Start => End
}
map task.2 {
Start => End
}
map task.3 {
Start => End
}
map task.4 {
Start => End
}
map task.5 {
Start => End
}
Kick.Off --> task.1 : Label 1
Kick.Off --> task.2 : Label 2
Kick.Off --> task.3 : Label 3
task.1 --> task.4
task.2 --> task.4
task.3 --> task.4
task.4 --> task.5 : Label 4
@enduml