trigger EsclateCase on Task (after insert) {
    list<CaseComment > cc = new list<CaseComment >();
    for(Task t : Trigger.new){
        string relatedTo = t.WhatId;
        Boolean IsRelatedToCase = relatedTo.startsWith('500');
        if(t.Escalated__c == true && IsRelatedToCase){
            CaseComment tempCC = new CaseComment(ParentId=relatedTo,CommentBody='This case is escalated');
            cc.add(tempCC );
        }
    }
    insert cc;
}