you should take a look at the dependencies feature. You will find it under "Settings -> All Settings" -> Manage Dependencies. If you have topology polling enabled on your network hardware, it will automatically discover some dependencies. But i would recommend you to check the discovered results. However you can define dependencies yourself. It can be nodes, interfaces, groups, applications etc.
Add a new dependencie and select the superior device. (example: CoreSwitch)
On the next screen select the subordinated devices (example: AccessSwitches)
Your alert "Node down" will then trigger only for the Core-Switch if this device is down. All depending devices will not be flagged as "down", they will be "not reachable".