How add new row for selected row in DataGrid Self-Reference Hierarchy by ContextMenu or add button

Dear Team,
I want to add new row by ContextMenu "Additem" or by add button for selected row

when using the feature of DataGrid inline edit in DataGrid Self-Reference Hierarchy
always appear new row in the first of grid,
How can add new row after row selected in DataGrid Self-Reference Hierarchy?

You can add the row to the collection assigned as DataGrid Data and execute Reload() for the DataGrid.

which I mean as example
when click Add row open new row below as below pic

when using feature for grid inline edit to add new row always add in the top of grid
because grid.InsertRow list.Insert(0,Item) look at pic below
image

To quote myself again.

Give me an example please.

Not sure what example you expect?! How to add an item in a collection? You can search the internet for details.