如何在am4charts中添加单个系列项目符号？

var chart = am4core.create("chartdiv", am4charts.XYChart);

var data = [
  {
    category: "Category 1",
    value: 10
  },
  {
    category: "Category 2",
    value: 20
  },
  // 其他数据项
];

var categoryAxis = chart.xAxes.push(new am4charts.CategoryAxis());
categoryAxis.dataFields.category = "category";

var valueAxis = chart.yAxes.push(new am4charts.ValueAxis());
valueAxis.renderer.minWidth = 20;

var series = chart.series.push(new am4charts.ColumnSeries());
series.dataFields.valueY = "value";
series.dataFields.categoryX = "category";

var bullet = series.bullets.push(new am4charts.CircleBullet());
bullet.circle.radius = 4; // 设置圆形符号的半径
bullet.fill = am4core.color("#ff0000"); // 设置符号的颜色

chart.data = data;
chart.invalidateData();