<mat-form-field>
  <mat-select placeholder="Pokemon" [formControl]="pokemonControl" multiple>
     <mat-option>-- None --</mat-option>
     <mat-optgroup *ngFor="let group of pokemonGroups" [value]="group.name"> Comment:- Need CheckBox for this value as well <mat-option *ngFor="let pokemon of group.pokemon" [value]="pokemon.value"> {{pokemon.viewValue}} </mat-option>
     </mat-optgroup>
   </mat-select>
 </mat-form-field>