The El cascade component clearcheckdnodes is invalid. Multiple multiple selection is set. If it is changed to single selection, expanding the lower level selection will be invalid for the first time. You cannot choose to turn off the lower level automatically

selectItem(i) {
if (i.length == 1) {
this.singleItem = i[0]
}
if (i.length > 1) {
let index = i.findIndex((v) => v === this.singleItem)
i.splice(index, 1)
this.form.category = ''
this.$nextTick(() => {
this.form.category = i
this.singleItem = i[0]
})
}
},

设计到赋值有下级的选项可以触发bug（插入不了视频演示）