- With the growing popularity of 3D printing, different shape classes such as fibers and hair have been shown, driving research toward class-specific solutions. Among them, 3D trees are an important class, consisting of unique structures, characteristics and botanical features. Nevertheless, trees are an especially challenging case for 3D manufacturing. They typically consist of non-volumetric patch leaves, an extreme amount of small detail often below printable resolution and are often physically weak to be self-sustainable. We introduce a novel 3D tree printability method which optimizes trees through a set of geometry modifications for manufacturing purposes. Our key idea is to formulate tree modifications as a minimal constrained set which accounts for the visual appearance of the model and its structural soundness. To handle non-printable fine details, our method modifies the tree shape by gradually abstracting details of visible parts while reducing details of non-visible parts. To guarantee structural soundness and to increase strength and stability, our algorithm incorporates a physical analysis and adjusts the tree topology and geometry accordingly while adhering to allometric rules. Our results show a variety of tree species with different complexity that are physically sound and correctly printed within reasonable time. The printed trees are correct in terms of their allometry and of high visual quality, which makes them suitable for various applications in the realm of outdoor design, modeling and manufacturing.