1<mat-menu #animals="matMenu">
2  <button mat-menu-item [matMenuTriggerFor]="vertebrates">Vertebrates</button>
3  <button mat-menu-item [matMenuTriggerFor]="invertebrates">Invertebrates</button>
4</mat-menu>
5
6<mat-menu #vertebrates="matMenu">
7  <button mat-menu-item [matMenuTriggerFor]="fish">Fishes</button>
8  <button mat-menu-item [matMenuTriggerFor]="amphibians">Amphibians</button>
9  <button mat-menu-item [matMenuTriggerFor]="reptiles">Reptiles</button>
10  <button mat-menu-item>Birds</button>
11  <button mat-menu-item>Mammals</button>
12</mat-menu>