The self-assembly formation of Zn/ZnO treelike nanostructures was achieved by simply aging the corresponding stable colloidal solution, produced by laser ablation in liquid, at room temperature without any further heating treatment. The self-assembled treelike structures consist of oriented attached nanoparticles with small misorientations and greatly improved crystallinity and exhibit significantly enhanced visible emission with two peaks in the blue and green regions, accompanying the decrease of the plasma resonance absorption of the core-part Zn nanocrystal. The self-assembly mechanism was attributed to the imperfect oriented attachment. The small misorientations among the attached nanoparticles were observed, and their accumulation guided the self-assembly formation of the multibranched nanostructures. As compensation for the insufficient driving force, adequate colloid stability and aging time were crucial for the accomplishment of the self-assembly process. This work could deepen the understanding of the nanocrystal self-assembly behavior, especially in the very “soft” environment, and the effect of the self-assembly process on the optical properties.