In the TreeTable, there are List Options for
setting the sort
column. Also, clicking on a column header sets
that column
as the "sorting column".

But from this point on, it's impossible to turn
off sorting again.

In my case, the original ("unsorted") node order
is important;
it's the order items were created. After sorting
by some other
columns (such as the "priority" column) you may
want to go back
to the original order, but currently you can't.
Sorting by column 0
isn't the same as unsorted.

I suggest you add "Do Not Sort" as an item in the
"Sort By" pullright menu.

I consider this a usability bug so have marked it
a defect rather
than a request for an enhancement.