Regroup hierarchical data/rearrange tree control

Question

I have advanceddatagrid with hierarchical data as input so that I can show tree table. Does anyone have an example of hot to rearrage and regroup tree? E.g. if my tree shows:

item 1
-- childitem 1
-- childitem 2
-- childitem 3
item 2
-- childitem 1
-- childitem 2

I would like the result to be:

childitem 1
-- item 1
-- item 2
childitem 2
-- item 1
-- item 2
childitem 3
-- item 1