When the secondary level tree is not expanded, here is how it looks like in 1.19:

But in 1.20 Insider, icons of two first level tree items "edgedevice" and "raspberrypi" are not aligned:

This issue can be temporarily worked around by selecting an icon theme other than the default "Seti" theme.

I see the issue, thanks for reporting. Will fix it soon.

Fixed it. Please try it out in tomorrows insiders.

I can verify the fix on macOS, but still reproduce the issue on Windows with the latest insiders

Version 1.20.0-insider
Commit 757ff83
Date 2018-01-29T05:13:39.772Z
Shell 1.7.9
Renderer 58.0.3029.110
Node 7.9.0
Architecture x64

@sandy081 Any updates? I can still reproduce this issue on Windows with the 2018-02-01's Insiders version.

@LazarusX Pushed some more fixes, please check with tomorrow's insiders. Thanks/

@sandy081 The issue can still be reproduced. The secondary level items are still closer to the left edge.

@LazarusX May I know which theme are you using?

Both the icon theme and the color theme are default (Seti/Default+). You can check my user settings below:

By the way, the issue can also be reproduced on macOS. Though I don't have access to my Windows machine at office right now, my settings on Windows and macOS are similar.

@LazarusX That's pretty bad. Fixed it.

@sandy081 Thanks for the quick fix! I can verify that my secondary level items are arranged correctly now.

However, for tree views with only first level items with icons, when switching between different icon themes, the items can move back and forth horizontally. Is it the expected behavior? See the "Docker Images" and "IoT Hub Devices" views below:

For tree views with multiple levels, the items will not move during icon theme switching.

@LazarusX Hmm.. I think it is not expected. We have similar experience in File explorer

Filed a new issue for that #43084.

Marking this as verified as user did.