ipsos-components/src/material-examples/select-optgroup/select-optgroup-example.html

Material Design components for Angular

<mat-form-field>
  <mat-select placeholder="Pokemon" [formControl]="pokemonControl">
    <mat-option>-- None --</mat-option>
    <mat-optgroup *ngFor="let group of pokemonGroups" [label]="group.name"
                  [disabled]="group.disabled">
      <mat-option *ngFor="let pokemon of group.pokemon" [value]="pokemon.value">
        {{ pokemon.viewValue }}
      </mat-option>
    </mat-optgroup>
  </mat-select>
</mat-form-field>