自定义一个树型的数据

 const tree = [{
    value: 1, label: "1",
    children: [{
      value: 11, label: "1-1",
      children: [{
        value: 111, label: "1-1-1"
      }]
    }]
  }, {
    value: 2, label: "2"
  }]

保留指定层级的方法

 function keepNodesAtLevel(data, level) {
    if (level == 1) {
      return data.map((node) => {
        return {
          value: node.value,
          label: node.label
        }
      })
    }
    let result = []
    for (let i = 0; i < data.length; i++) {
      let node = data[i]
      if (node.children) {
        node.children = keepNodesAtLevel(node.children, level - 1)
      }
      result.push(node)
    }
    return result
  }

console.log(keepNodesAtLevel(tree, 1))