trigger Campaign_Accounts_After on Campaign_Accounts__c (after insert, after delete, after undelete) {

//1. Update Campaign Number of Accounts in Campaign and Parent Campaigns
if(trigger.isInsert || trigger.isUpdate){
    //List<Campaign> parentCampaignsUpdate = new List<Campaign>();
    Set<Id> associatedCampaignIds = new Set<Id>();
    for(Campaign_Accounts__c campaignAccounts : Trigger.new){
        associatedCampaignIds.add(campaignAccounts.Campaign__c);
    }

    List<AggregateResult> campaignAccountsCount = [SELECT Campaign__c, COUNT(Account__c) FROM Campaign_Accounts__c WHERE Campaign__c IN : associatedCampaignIds GROUP BY Campaign__c];

    List<Campaign> campaignsUpdate= new List<Campaign>();
    for(AggregateResult ar : campaignAccountsCount){
        Campaign c = new Campaign();
        //System.debug(ar.get('expr0'));
        c.Accounts_in_Campaign__c = (Integer)ar.get('expr0');
        //c.HierarchyNumberOfAccounts__c = c.Accounts_in_Campaign__c; //for this also I need to iterate all the child campaigns
        c.Id = (Id)ar.get('Campaign__c');
        campaignsUpdate.add(c);

    }
    update campaignsUpdate;

    //Maintain the hierarchy, search for parents
    for (Campaign campaign : [SELECT Accounts_in_Campaign__c, HierarchyNumberOfAccounts__c, ParentId FROM Campaign WHERE Id IN :campaignsUpdate])
    {
        Campaign childCampaign = new Campaign();
        if(campaign.ParentId != null){
            // In this foor loop: I need to write SOQL to get the Parent Campaign Details and check if Parent has further a parent Campaign or not.
            // I am lost here.
        }
    }
}