Solution
Custom glyphs can be added to trees and listboxes using the Custom Item Symbols:Set To Custom Symbol method. You can use this method with any image files, including the LabVIEW-specific icons in the following folder:
[LabVIEW 20xx]\resource\Framework\Providers\Icons
The following are examples for the different controls:

Note: This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project. To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW diagram.
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Listbox

Note: This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project. To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW diagram.

Note: This image is a LabVIEW snippet, which includes LabVIEW code that you can reuse in your project. To use a snippet, right-click the image, save it to your computer, and drag the file onto your LabVIEW diagram.