棵树的底部是圆柱体，顶部是圆锥体。</p>
        <p>第一步，我们创建圆锥体和圆柱体的Geometry和Material，所有的树都会复用这些。</p>
        <pre class="prettyprint showlinemods notranslate lang-js" translate="no">
const trunkRadius = .2;
const trunkHeight = 1;
const trunkRadialSegments = 12;
const trunkGeometry = new THREE.CylinderGeometry(
    trunkRadius, trunkRadius, trunkHeight, trunkRadialSegments);

const topRadius = trunkRadius * 4;
const topHeight = trunkHe