The problem with your original model seems to be that the tree item you sent to Show does not originate from (and refers to) the display, but is rather the one created to be sent (and copied) to the display.
While composite data elements are handled by reference (display elements are also composite data elements), sending them to the display causes an implicit copy of the content to a new (display) reference.
The fix should be along the lines of JP's suggestion, of finding the tree item element in the display. Or alternatively, you could output the tree item element from it's parent display reference immediately on adding it to the display, as in the following screenshot:
(this would work, as the new item added in this way to a repetition is always the last element in the repetition, and so the outgoing flow will send it as the last, and therefore the the only, element handled by the non-repetitive Show)
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