angular material multi select ngmodel

<mat-form-field>
    <mat-select [compareWith]="compareFn" name="users" [(ngModel)]="users" multiple>
        <mat-option *ngFor="let person of people" [value]="person">
           {{ person.username }}
        </mat-option>
   </mat-select>
</mat-form-field>

compareFn(user1: User, user2: User) {
    return user1 && user2 ? user1.id === user2.id : user1 === user2;
}