1-inch-wide painter's tape
White latex paint
Apply painter's tape in 2-inch sections vertically on the wall to create the tree trunks. Applying the tape in small sections will make your lines less rigid and more organic.
Cut 1/2- to 2-inch lengths of tape and small triangles. Apply them horizontally at random intervals (right).
Working inside the taped lines, brush on one light coat of white latex paint (right). Don't worry about getting an even coat. The uneven coverage gives the tree texture and dimension.