When I use this code: 

**jQuery:**

```
$(this).next().slideDown()

```

of a selector :`$(this).next()`

**HTML:**

```
<li class="sub-menu two-level-collapse">
                    <a href="javascript:void(0);" class="two-level-collapse parent"><i
                            class="fa fa-line-chart"></i><span>Quản lý dữ liệu trạm</span><i
                            class="arrow fa fa-angle-right pull-right"></i></a>
                    <ul class="two-level-collapse">
                        <li class="sub-menu two-level-collapse">
                            <a class="two-level-collapse" id="sub-sub-a" href="javascript:void(0);">
                                <i></i><span>cem</span><i class="arrow fa fa-angle-right pull-right"></i></a>
                            <ul class="two-level-collapse">
                                <li class="two-level-collapse"><a
                                        href='{{pathFor route='manager.csv' query='type=humid_cem'}}'>humid_cem</a></li>
                                <li class="two-level-collapse"><a
                                        href='{{pathFor route='manager.csv' query='type=temp_cem'}}'>temp_cem</a></li>
                                <li class="two-level-collapse"><a href='{{pathFor route='manager.csv'
                                                                                  query='type=rainfall_cem'}}'>rainfall_cem</a>
                                </li>
                            </ul>
                        </li>
                        <li class="sub-menu two-level-collapse">
                            <a class="two-level-collapse" id="sub-sub-a" href="javascript:void(0);">
                                <i></i><span>kttvtw</span><i class="arrow fa fa-angle-right pull-right"></i></a>
                            <ul class="two-level-collapse">
                                <li class="two-level-collapse"><a href='{{pathFor route='manager.csv'
                                                                                  query='type=humid_kttvtw'}}'>humid_kttvtw</a>
                                </li>
                                <li class="two-level-collapse"><a
                                        href='{{pathFor route='manager.csv' query='type=temp_kttvtw'}}'>temp_kttvtw</a>
                                </li>
                                <li class="two-level-collapse"><a
                                        href='{{pathFor route='manager.csv' query='type=rainfall_kttvtw'}}'>rainfall_kttvtw</a>
                                </li>
                            </ul>
                        </li>
                        <li class="sub-menu two-level-collapse">
                            <a class="two-level-collapse" id="sub-sub-a" href="javascript:void(0);">
                                <i></i><span>global</span><i class="arrow fa fa-angle-right pull-right"></i></a>    
                        </li>
                    </ul>
                </li>

```

It expands all sub-level of `$(this).next()`  

Like that: [demo](https://www.w3schools.com/code/tryit.asp?filename=FMWT6CS9GEPP)

How can I slide down just one level of element 's children, not sub-levels?
Thank you in advanced!