code: function (node, startAngle) {
              if (!node) {
                  return;
              }
  
              var endAngle = startAngle;
  
              // Render self
              if (node !== virtualRoot) {
                  // Tree node is virtual, so it doesn't need to be drawn
                  var value = node.getValue();
  
                  var angle = (sum === 0 && stillShowZeroSum)
                      ? unitRadian : (value * unitRadian);
                  if (angle < minAngle) {
                      angle = minAngle;
                      restAngle -= minAngle;
                  }
                  else {
                      valueSumLargerThanMinAngle += value;
                  }
  
                  endAngle = startAngle + dir * angle;
  
                  var depth = node.depth - rootDepth
                      - (renderRollupNode ? -1 : 1);
                  var rStart = r0 + rPerLevel * depth;
                  var rEnd = r0 + rPerLevel * (depth + 1);
  
                  var itemModel = node.getModel();
                  if (itemModel.get('r0') != null) {
                      rStart = parsePercent(itemModel.get('r0'), size / 2);
                  }
                  if (itemModel.get('r') != null) {
                      rEnd = parsePercent(itemModel.get('r'), size / 2);
                  }
  
                  node.setLayout({
                      angle: angle,
                      startAngle: startAngle,
                      endAngle: endAngle,
                      clockwise: clockwise,
                      cx: cx,
                      cy: cy,
                      r0: rStart,
                      r: rEnd
                  });
              }
  
              // Render children
              if (node.children && node.children.length) {
                  // currentAngle = startAngle;
                  var siblingAngle = 0;
                  zrUtil.each(node.children, function (node) {
                      siblingAngle += renderNode(node, startAngle + siblingAngle);
                  });
              }
  
              return endAngle - startAngle;
          }
docs: Render a tree
  @return increased angle