A plant is having an undivided main stem or trunk, as the spruce and other conifers. If a side branch begins growing upright in a trunk-like fashion, prune it back, redirecting growth to an outward direction. Do not prune or head back the central leader (trunk). The desired branching structure depends on the natural growth habit of the tree. Trees with an excurrent growth habit develop with a central leader (single trunk) to the top. Examples of excurrent trees include Aspen, Linden and pines.