Help with ComponentOne's flexgrid.subtotal() function to create simple tree (vb.net)

I have a simple datatable called myDatatable which looks something like this:

APPLES, GALA
APPLES, MACINTOSH
APPLES, GOLDEN
ORANGES, MANDARIN
ORANGES, DECORATIVE

I want to use ComponentOne's flexgrid to turn this into a tree.  Meaning the APPLES and ORANGES are each compressed to one line like:

+APPLES
+ORANGES

And clicking on the + will expand the tree.  I've read the flexgrid documentation and looked for examples.  It appears the following code will be the beginning of what I need.  Where I need help is with the Subtotal() line.... not sure how to structure it and I can't find relative examples.

myFlexgrid is already on my form and ready to use.  It's default state.  I haven't changed any properties.  myDatatable is already populated with two columns of text data.

myFlexgrid.DataSource = myDatatable
myFlexgrid.Tree.Column = 0  'I understand this will put the + in the first column.. right?
myFlexgrid.Tree.Style = TreeStyleFlags.Simple

'And now the line I'm not sure how to format
myFlexgrid.Subtotal(??????)

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Any insights would be very much appreciated.  Thank you!