ElementUI 折叠tree全部节点

      // tree为Tree组件的ref值，isexpand为true或false
        this.$nextTick(() => {
          for(let i=0;i<this.$refs.tree.store._getAllNodes().length;i++){
            this.$refs.tree.store._getAllNodes()[i].expanded=false;
          }
        });

参考：https://www.jianshu.com/p/15666261e377