JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="dropdown">
    <li><a href="#">Item 1</a>
        <ul>
            <li><a href="#">Subitem 1</a></li>
            <li><a href="#">Subitem 2</a></li>
            <li><a href="#">Subitem 3</a>
                <ul>
                    <li><a href="#">Subsubitem 1</a></li>
                    <li><a href="#">Subsubitem 2</a></li>
                    <li><a href="#">Subsubitem 3</a></li>
                </ul>
            </li>
        </ul>
    </li>
    <li><a href="#">Item 2</a></i>
    <li><a href="#">Item 3</a>
        <ul>
            <li><a href="#">Subitem 1</a></li>
            <li><a href="#">Subitem 2</a></li>
            <li><a href="#">Subitem 3</a>
                <ul>
                    <li><a href="#">Subsubitem 1</a></li>
                    <li><a href="#">Subsubitem 2</a></li>
                    <li><a href="#">Subsubitem 3</a></li>
                </ul>
            </li>
        </ul>
    </li>
</ul>

CSS

* {
    margin: 0px;
    padding: 0px;
}

a, a:visited {
    color: orange;
    text-decoration: none;
}

body {
    font-family: 'Ubuntu';   
    padding: 50px;
}

ul ul {
   display: none;
    border: 1px solid red;
}

ul ul ul {
    border: 1px solid blue;   
}
}

ul {
    width: 200px;   
}

li {
    position: relative;
    border-bottom: 1px solid #eee;
    list-style: none;
}

.plus {
    height: 10px;
    width: 10px;
    background: grey;
    position: absolute;
    right: 0;
    color: #fff !important;
    top: 0;
    font-size: 8px;
    text-align: center;
    text-decoration: none;
}

JavaScript

$('.dropdown li').each(function(e) {
    
	if($(this).children("ul").length) {
		$(this).append('<a href="#" class="plus">+</a>');
   }
	
});

$('.plus').click(function(e){
   
    e.preventDefault();
    
    $('ul ul').slideUp();  
    $('li').removeClass('active');
    
    $(this).parent('li').find('> ul').slideDown();
    $(this).parent('li').addClass('active');
    
});