Calling Batch class with Salesforce Apex Trigger

trigger ProcessStage on Stage__c (after insert) {

Database.executeBatch(new BatchProcessStage(trigger.newMap.keySet()),200);
}

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public class ProcessStaging{
public static void handleafterInsert(List<Stage__c> listStage){
Map<String ,Contact> contactMap = new Map<String ,Contact>();
Map<String ,Id> accountMap = new Map<String ,Id>();
Set<String>fname = new Set<String>();
Set<String>orgname = new Set<String>();
List<Contact> insertContact = new List<Contact>();
List<Contact> relatedContact = new List<Contact>();
List<Contact> finalContactinsert = new list<Contact>();
List<Opportunity> opportunityContact = new List<Opportunity>();
List<Opportunity> opportunityAccount = new List<Opportunity>();
List<Opportunity> relatedOpportunity = new List<Opportunity>();
List<Account> insertAccount = new List<Account>();
List<Contact> finalcontact = new List<Contact>();

for(Stage__c st :listStage) {
fname.add(st.First_Name__c);
fname.add(st.Last_Name__c);
fname.add(st.Postal_Code__c);
orgname.add(st.Organisation_Name__c);
orgname.add(st.Postal_Code__c);
}
List<Contact> conlist = [select Id,FirstName,LastName,MailingPostalCode from contact where (FirstName IN:fname) AND (LastName IN:fname) AND (MailingPostalCode IN:fname) ];
List<Account> acclist = [select Id,Name,BillingPostalCode from account where (Name IN:orgname) AND (BillingPostalCode IN:orgname) ];
system.debug('aaaa' +conlist);
system.debug('acclist' +acclist);

for(Contact con : conlist) {
contactMap.put(con.firstname +'_'+ con.lastname+'_'+ con.MailingPostalCode,con );
// contactMap.put(con.firstname,con );
}

for(Account ac : acclist) {

accountMap.put(ac.Name +'_'+ ac.BillingPostalCode,ac.id );

}

for(Stage__c st :listStage) {
Id accs;

if(st.Individual_Or_Organisation__c=='I'){

if(!contactMap.containsKey(st.First_Name__c+ '_' +st.Last_Name__c+ '_' +st.Postal_Code__c )) {

// if(!contactMap.containsKey(st.First_Name__c)) {
Contact cc =new Contact();
cc.firstname=st.First_Name__c;
cc.lastname=st.Last_Name__c;
cc.OtherPostalCode =st.Postal_Code__c;
// insertContact.add(cc);
system.debug(insertContact +'listtttt');

if(st.Organisation_Name__c!='' && st.Postal_Code__c!='' && accountMap.containsKey(st.Organisation_Name__c+ '_' +st.Postal_Code__c)) {

system.debug('hellohey');

system.debug('aaa' +accountMap.get(st.Organisation_Name__c+ '_' +st.Postal_Code__c));
cc.accountId = accountMap.get(st.Organisation_Name__c+ '_' +st.Postal_Code__c);
system.debug('######'+''+accs);
// cc.accountId = accs;

}
insertContact.add(cc);
Opportunity op= new Opportunity();
op.name= cc.firstname;
op.CloseDate= st.Date_Received__c;
op.StageName='prospecting';
op.AccountId=accountMap.get(st.Organisation_Name__c+ '_' +st.Postal_Code__c);
opportunityContact.add(op);
}
}
else if(st.Individual_Or_Organisation__c=='O') {
if(!accountMap.containsKey(st.Organisation_Name__c+ '_' +st.Postal_Code__c)) {
Account ac1 = new Account();
ac1.Name=st.First_Name__c;
insertAccount.add(ac1);
system.debug(opportunityAccount +'case2op');
if(st.Last_Name__c!='' && st.Postal_Code__c!='' && contactMap.containsKey(st.First_Name__c+ '_' +st.Last_Name__c+ '_' +st.Postal_Code__c) ){

system.debug('lstloop');
Contact cntt = new Contact();
cntt = contactMap.get(st.First_Name__c+ '_' +st.Last_Name__c+ '_' +st.Postal_Code__c);
cntt.Account =ac1;
finalContactinsert.add(cntt);
system.debug('finalContactinsert'+ finalContactinsert);

}
Opportunity op1= new Opportunity();
op1.Account= ac1;
op1.name =ac1.Name;
op1.CloseDate= st.Date_Received__c;
op1.StageName='prospecting';
opportunityAccount.add(op1);

}

}
}

if(insertContact.size()>0) {
insert insertContact;
}
if(opportunityContact.size()>0) {
upsert opportunityContact;
}
if(insertAccount.size()>0) {
insert insertAccount;
}

for(Contact con :finalContactinsert) {

con.Accountid = con.Account.id;
system.debug(con.Accountid +'contact accountid');
system.debug(con.Account.id +'id of account');
relatedContact.add(con);
system.debug('relation'+relatedContact);
system.debug('relatedContact' +relatedContact);
}
if(relatedContact.size()>0) {
upsert relatedContact;
}
for(Opportunity op :opportunityAccount) {

op.Accountid = op.Account.id;
system.debug(op.Accountid +'contact accountid');
system.debug(op.Account.id +'id of account');
relatedOpportunity.add(op);
system.debug('relatedOpportunity' +relatedOpportunity);
}
if(relatedOpportunity.size()>0) {

upsert relatedOpportunity;
}

}
}

******************
global class BatchProcessStage implements Database.Batchable<Sobject> {

Public string soqlquery;
Set<Id>sid= new Set<Id>();

public BatchProcessStage (Set<id> sid){
this.sid = sid ;
}

Public void setQry(string soqlquery){
this.soqlquery = 'Select First_Name__c,Last_Name__c,Postal_Code__c,Organisation_Name__c,Individual_Or_Organisation__c from stage where id in : sid';
}

global database.querylocator start(database.batchableContext bc){
return database.getquerylocator(soqlquery);
}

global void execute(database.batchablecontext bd, List<Stage> stglist){
ProcessStaging.handleafterInsert(stglist);
}

Public void finish(database.batchableContext bc){
}

}

Error: Compile Error: Class BatchProcessStage must implement the method: void Database.Batchable<SObject>.execute(Database.BatchableContext, List<SObject>) at line 1 column 14