The wood / tree radical on the left places 树 in the family of plants and timber: 林 forest, 桥 bridge, 桌 desk, 椅 chair. Compressed into a slim left-side form so the bulky right side has room.
Simplified replacement for the traditional right side 尌 (a hand 寸 planting). 对 supplies an approximate sound and keeps 寸 (hand) at the bottom-right, faintly preserving the planting gesture inherited from 樹. Sound has drifted: duì vs shù.
