Table Grouping showing checkbox instead of dropdown carat

[latha-karbonhq]

I have a simple table with children like shown in the docs: https://opensource.addepar.com/ember-table/docs/guides/body/rows-and-trees.
What I expected was the table with grouping and dropdown carat to indicate the expand / collapse state. but what I see is like this:

Clicking on the checkbox does collapse and expand, but what I want is an inline dropdown carat instead of checkbox

My code:

<EmberTable as |t|>
    <t.head @columns={{this.columns}} @widthConstraint='gte-container' as |h|>
      <h.row as |r|>
        <r.cell as |column|>
          {{column.name}}
        </r.cell>
      </h.row>
    </t.head>

    <t.body @rows={{this.rows}} as |b|>
      <b.row as |r|>
        <r.cell as |value|>
          {{value}}
        </r.cell>
      </b.row>
    </t.body>
  </EmberTable>

[latha-karbonhq]

Is there any prop that I am missing?

[latha-karbonhq]

Seeing this PR: https://github.com/Addepar/ember-table/pull/532/files seems like this is how it is modified, How can I overwrite this checkbox to dropdown carat?