Perhaps, you mean "indented text syntax" instead of "PlantUML syntax", something like tree-widjet in PlantUML, but marked jaust with indents and rendered as a graph.
So, this should be a the neato, not the dot renderer - as it's a force graph, not a tree.
So, as far, as I can understand possible realisation, this could be something like this:
@startuml
mindmap
Root Item
Item 1
Item 1.1
Item 2
@enduml