手動設置el-tree展開與收起

<el-tree
              :data="projectTree"
              :check-strictly="relationParent"
              show-checkbox
              default-expand-all
              node-key="id"
              ref="ProjectTree"
              highlight-current
              :props="defaultProps"
              :filter-node-method="filterNode"
            >
            </el-tree>

expandAll(bool) {
      var nodes = this.$refs.ProjectTree.store.nodesMap;
      for (var i in nodes) {
        nodes[i].expanded = bool;
      }
    }