When I am trying TreeGridExample from here
I get the tree with + expand-collapse icon. How can I change it to arrow icon like |>? I just want to is it customisable too or not.
The icon comes from the TreeImagePainter that is wrapped in a IndentedTreeImagePainter which is configured via cell painter style. To answer the question, yes it is possible.
You might want to have a look at the ThemeConfiguration and the subclasses to see what styles can be adjusted and how.