Whenever Opportunity stagename fieldset to 'Closed Won', a new record has created in patient object

trigger newpatient on Opportunity (after update) {
    Map<Id,Patient__c> patients = new Map<Id,Patient__c>();
    for(Integer i=0;i<Trigger.new.size();i++) {
        if(Trigger.new[i].StageName != Trigger.old[i].StageName && 

Trigger.New[i].StageName == 'Closed Won') {
            Patient__c p = new Patient__c(name='p101',Patient_Name__c='srinu',

Country__c='India',DOB__c=Date.valueOf('1987-07-18'),Opportunity__c=Trigger.new[i].id);
            patients.put(p.id,p);            
            }            
        }
        insert patients.values();
    }

Reference:

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