Например так...
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<!--
<script src="https://code.jquery.com/jquery-latest.min.js" type="text/javascript"></script>
-->
<style>
.box > div {
display: none;
}
</style>
<script>
document.addEventListener('DOMContentLoaded', _ => {
})
</script>
</head>
<body>
<div id="6" class="comment" data-parent="0" data-level="1">...</div>
<div class='box'>
<a href='#'>Смотреть все</a>
<div id="7" class="comment" data-parent="6" data-level="2">...</div>
<div id="8" class="comment" " data-parent="6" data-level="2">...</div>
<div id="9" class="comment" " data-parent="6" data-level="2">...</div>
</div>
<div id="10" class="comment" data-parent="0" data-level="1">...</div>
<div class='box'>
<a href='#'>Смотреть все</a>
<div id="11" class="comment" data-parent="10" data-level="2">...</div>
<div id="12" class="comment" data-parent="10" data-level="2">...</div>
<div id="13" class="comment" data-parent="10" data-level="2">...</div>
</div>
</body>
</html>