The conversion heavily dials down the apparent contrast between the leaves and the trunks (aka "looks flat"). You could fix this in various ways - by using tone controls or the luminosity of the colors or restoring a bit of color in the leaves. If you want to retain texture in the leaves you could try different luminosities for yellow and green. Having said all that, the color version is pretty bichromatic anyway and looks really nice to me - symmetrical but not too symmetrical.