You can also use the LEVELS adjustment to get the results as shown and to adjust accordingly with the tutorial posted below.
Switching the output sliders to opposite ends will give you the opposite of the image below (white tree on black). You can INVERT the image (black tree on white) but the results may need a bit more work depending on what you started out with. It's a matter of preference depending on the end result you want to achieve. I personally prefer using the Threshold adjustment on certain selection creation needs ........
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I finally found an image appropriate to use with the earlier posted technique.... I prefer doing this directly on the image duplicate.... less hassles... lol.
Duplicate the layer and apply the Threshold adjustment. Zoom up to the tree so you can see the effect on the branches and adjust as needed. If you think it looks perfect enough, apply it.
As you can see above, the rest of the image is not perfect but that can be fixed by brushing white on the background areas to retouch it the way I want it to look. This is like choreographing the result to what you intend it for. You may also need a bit of brightness and contrast adjustments to get the blackest black and whitest white.
Photoshop Gurus Tip :
Black hides, White Reveals and any level of gray in between will affect the transparency effect of the mask. Remember this when editing a Layer Mask.
Select the black pixels of the tree. I did this by selecting the white background then press CTRL+I to inverse the selection...
It's now a matter of adding a vector mask to another duplicate of the original image. Hide your Threshold layer and click the duplicate to make it the active layer and add the Vector mask as shown.....
That's all there is. What's left now is how you'll use it....
For this I used the original background image, made it an editable layer, flipped it horizontally and VIOLA.....
With a bit of retouch on the mask layer to hide parts of the tree's shadow to match the source light on the original. it's good to go....
Enjoy.....