Bootstrap button group inside vertical button group

I'd like to create a vertical button group, containing a horizontal button group, and a few buttons inside. My attempt looks like this:

  <div class="btn-group-vertical">
    <div class="btn-group">
       <button type="button" class="btn btn-primary" style="width : 60%">Row 1.1</button>
       <button type="button" class="btn btn-primary" style="width : 40%">Row 1.2</button>
    </div>
    <button type="button" class="btn btn-primary">Row 2</button>
    <button type="button" class="btn btn-primary">Row 3</button>
  </div>

I want button Row 1.1 and Row 1.2 to be in one row.

Enclose your button group in a row class:

<div class="row">
    <div class="btn-group">
        <button type="button" class="btn btn-primary" style="width : 60%">Row 1.1</button>
        <button type="button" class="btn btn-primary" style="width : 40%">Row 1.2</button>
    </div>
</div>

Check the Codepen. You might wanna change the width/border the way you want it.

EDIT

As for the buttons not being rounded, here's the class responsible for it, you can change it:

.btn-group-vertical > .btn:not(:first-child):not(:last-child) {
    border-radius: 0;
}

From bootstrap.css, the btn class has a border-radius: 4px :

.btn {
    ...
    border: 1px solid transparent;
    border-radius: 4px;
}

You can either remove all the radius or change the second button to have the same border-radius

New Codepen