dropdown (Dx-tag-box)

Question

I have a dropdown (Dx-tag-box) created in Angular Devextreme with Typescript, which comes with the data from the server.

 <label for="incomeProspects" class="font-weight-bold">Servizi</label>
                      <dx-tag-box [items]="servizi" [visible]="true" [showSelectionControls]="true" displayExpr="value"
                        valueExpr="key" noDataText="Questo campo non contiene dati!" [searchEnabled]="true"`your text`
                        [showClearButton]="true" [showDropDownButton]="true">
                      </dx-tag-box>.

and button 
<dx-button class="buttonToLink"  text="Include Nascoste "
                  `your text`      (onClick)="moreButton()">
                      </dx-button>

How to add this button inside the drop down menu? The model would be like this