What I decided to do for my demonstration painting of hadaka no ki (winter trees) and fuyu no ki (bare trees) is to paint a combination of three different types of tree; horse chestnut, white birch, and weeping willow. Each has distinctive shapes and other characteristics.
My painting uses mostly sumi with the exception of a couple of touches of gansei (colored ink). Remember that the darkest sumi is generally used for foreground objects and lighter sumi for distant objects to give paintings a feeling of depth. There are exceptions, however. The bark of birch trees is naturally very light in color, so if you want to accurately represent birches, light sumi should be used regardless of where they are placed. But the paintings you produce are yours, and you can choose to do something different if you wish. Be creative. I decided to add a squirrel looking at horse chestnut fruit for added interest.
Here is my demonstration painting.