Trees in retro 3D games have weird shading mainly due to early hardware limitations that restricted complex lighting and high-quality textures.
Retro systems used simple flat shading (for speed) on low-polygon tree models, causing harsh, unblended shadows. Low-resolution textures also made shading look blocky or mismatched.
To recreate retro tree shading, use flat shading (e.g., in Blender) and keep textures low-res—this stays true to the era’s constraints without overcomplicating.