Sabyasachi,

This is almost 5 years late but you can add this into a Script Editor above or below a list view. It will add a + or - to the right of the View menu. Clicking the + will expand groups.

• You might need to experiment with the jQuery version
• See the source comments mid way through to see where I got this
• I have used this in SP2013 and SP2019

<script  src="https://code.jquery.com/jquery-3.7.1.min.js"
  integrity="sha256-/JqT3SQfawRcv/BIHPThkBvs0OEvtFFmqPF/lYI/Cxo="
  crossorigin="anonymous"></script>
<script type="text/javascript">

    function expandAll() {

        $("img.ms-commentexpand-icon").click();

    }

    function collapseAll() {

        $("img.ms-commentcollapse-icon").click();

    }

    var expandButton = "<a href='#' onClick="

    +'"' + "this.href='javascript:expandAll()'"

    + '">&nbsp;<img title="expand all groups" style="border:none;" alt="expand all" src="/_layouts/images/advadd.png" width="15" height="15"></a>';

    var collapseButton = "<a href='#' onClick="

    +'"' + "this.href='javascript:collapseAll()'"

    + '">&nbsp;<img title="expand all groups" style="border:none;" alt="collapse all" src="/_layouts/images/advminus.png" width="15" height="15"></a>';

    $(document).ready(function () {

        $(".ms-pivotControl-container").append(expandButton).append(collapseButton);

    });

// Source:  http://www.sharepointdiary.com/2014/07/expand-collapse-all-groups-in-sharepoint-2013-list-view-jquery.html


ExecuteOrDelayUntilScriptLoaded(overrideSurfacePivotCount, 'clienttemplates.js');

function overrideSurfacePivotCount() {
   ClientPivotControl.prototype.SurfacedPivotCount = 10;
};
</script> 

This is almost 5 years late but you can add this into a Script Editor above or below a list view. It will add a + or - to the right of the View menu. Clicking the + will expand groups.

• You might need to experiment with the jQuery version
• See the source comments mid way through to see where I got this
• I have used this in SP2013 and SP2019

<script  src="https://code.jquery.com/jquery-3.7.1.min.js"
  integrity="sha256-/JqT3SQfawRcv/BIHPThkBvs0OEvtFFmqPF/lYI/Cxo="
  crossorigin="anonymous"></script>
<script type="text/javascript">

    function expandAll() {

        $("img.ms-commentexpand-icon").click();

    }

    function collapseAll() {

        $("img.ms-commentcollapse-icon").click();

    }

    var expandButton = "<a href='#' onClick="

    +'"' + "this.href='javascript:expandAll()'"

    + '">&nbsp;<img title="expand all groups" style="border:none;" alt="expand all" src="/_layouts/images/advadd.png" width="15" height="15"></a>';

    var collapseButton = "<a href='#' onClick="

    +'"' + "this.href='javascript:collapseAll()'"

    + '">&nbsp;<img title="expand all groups" style="border:none;" alt="collapse all" src="/_layouts/images/advminus.png" width="15" height="15"></a>';

    $(document).ready(function () {

        $(".ms-pivotControl-container").append(expandButton).append(collapseButton);

    });

// Source:  http://www.sharepointdiary.com/2014/07/expand-collapse-all-groups-in-sharepoint-2013-list-view-jquery.html


ExecuteOrDelayUntilScriptLoaded(overrideSurfacePivotCount, 'clienttemplates.js');

function overrideSurfacePivotCount() {
   ClientPivotControl.prototype.SurfacedPivotCount = 10;
};
</script>