A conversion using the Filter/Adjustments/Gradient Map, with the choice of Black and White.

It seems to be a very “true conversion” if I flip between the original colour and this B&W image there is the dropout of colour but the tones and density seem to remain true to the original. The shadows on both are dark and similar on the branches as are the leaves.

I have used this method a number of times and get a good B&W image for a range of colour subjects. It gives me a similar result to Enhance/Adjust Colour/Remove Colour. There is a difference in that the Gradient Map results in warm grays and the Remove Colour gives me cool grays.

Note that the above is my experience with my computer and my images and may not be always be the case.