Collapse作用：
		折叠，如左侧各级菜单栏折叠。

Collapse工作原理：
		将元素的高度变为0（感兴趣的可以去看源码）

Collapse使用：
		class="collapse" 将要折叠的内容声明为collapse类
		通过按钮控制折叠（非按钮如链接a可以声明role="button"）

Collapse选项：（处于按钮中）
		data-bs-toggle="collapse" （绑定collapse事件）
		data-bs-target="#target" （折叠的目标，可用id选择器或class选择器）
		aria-expanded="false" （true为默认展开，false为默认折叠）
		aria-controls="target" （控制的元素，可填多个id，空格隔开）

		（处于折叠元素中）
				data-bs-parent="#parent" （父元素，组管理功能，如点击展开二级目录其他目录折叠）

示例：
<p>
  <a class="btn btn-primary" data-bs-toggle="collapse" href="#multiCollapseExample1" role="button" aria-expanded="false" aria-controls="multiCollapseExample1">Toggle first element</a>
  <button class="btn btn-primary" type="button" data-bs-toggle="collapse" data-bs-target="#multiCollapseExample2" aria-expanded="false" aria-controls="multiCollapseExample2">Toggle second element</button>
  <button class="btn btn-primary" type="button" data-bs-toggle="collapse" data-bs-target=".multi-collapse" aria-expanded="false" aria-controls="multiCollapseExample1 multiCollapseExample2">Toggle both elements</button>
</p>
<div class="row">
  <div class="col">
    <div class="collapse multi-collapse" id="multiCollapseExample1">
      <div class="card card-body">
        Some placeholder content for the first collapse component of this multi-collapse example. This panel is hidden by default but revealed when the user activates the relevant trigger.
      </div>
    </div>
  </div>
  <div class="col">
    <div class="collapse multi-collapse" id="multiCollapseExample2">
      <div class="card card-body">
        Some placeholder content for the second collapse component of this multi-collapse example. This panel is hidden by default but revealed when the user activates the relevant trigger.
      </div>
    </div>
  </div>
</div>

下面是我自己试验用的，使用JS将JSON生成菜单，生成的HTML代码如：
<div id="parent">
                    <div id="first_menu">

                        <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#second_menu" aria-expanded="false" aria-controls="second_menu" type="button">一级菜单</button></h2>
                        <div class="p-5 collapse second_menu" id="second_menu" data-bs-parent="#first_menu">
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_1" aria-expanded="false" aria-controls="third_menu_1" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_1" data-bs-parent="#second_menu">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_2" aria-expanded="false" aria-controls="third_menu_2" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_2" data-bs-parent="#second_menu">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_3" aria-expanded="false" aria-controls="third_menu_3" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_3" data-bs-parent="#second_menu">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                        </div>


                        <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#second_menu1" aria-expanded="false" aria-controls="second_menu1" type="button">一级菜单</button></h2>
                        <div class="p-5 collapse second_menu" id="second_menu1" data-bs-parent="#first_menu">
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_11" aria-expanded="false" aria-controls="third_menu_11" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_11" data-bs-parent="#second_menu1">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_21" aria-expanded="false" aria-controls="third_menu_21" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_21" data-bs-parent="#second_menu1">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_31" aria-expanded="false" aria-controls="third_menu_31" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_31" data-bs-parent="#second_menu1">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                        </div>

                        <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#second_menu2" aria-expanded="false" aria-controls="second_menu2" type="button">一级菜单</button></h2>
                        <div class="p-5 collapse second_menu" id="second_menu2" data-bs-parent="#first_menu">
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_12" aria-expanded="false" aria-controls="third_menu_12" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_12" data-bs-parent="#second_menu2">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_22" aria-expanded="false" aria-controls="third_menu_22" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_22" data-bs-parent="#second_menu2">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                            <h2><button class="btn btn-primary" data-bs-toggle="collapse" data-bs-target="#third_menu_32" aria-expanded="false" aria-controls="third_menu_32" type="button">二级菜单</button></h2>
                            <div class="p-5 collapse third_menu" id="third_menu_32" data-bs-parent="#second_menu2">
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                                <h2><button class="btn btn-primary">三级菜单</button></h2>
                            </div>
                        </div>



                    </div>
                </div>