Trees 3D models often have weird shading in flat shade because flat shading applies a single color per face, which conflicts with the dense, overlapping small faces (like leaves or fine branches) typical of tree geometry.
Flat shading doesn’t blend vertex colors, so each tiny tree face shows a harsh, unconnected edge—trees rely on smooth blending to look natural, so flat shading breaks that coherence and creates patchy or jagged results.
If you’re seeing this, try merging small adjacent faces (e.g., leaf clusters) or using a mix of flat and smooth shading (e.g., flat for branches, smooth for leaves) to reduce unnatural edges without losing detail.