Give Sample Code Snippet of Salesforce Apex which shows how Parent and Child record can be inserted in a Statement?

It can be done with help of External Id.

Date dt = Date.today().addDays(7);
Opportunity newOpportunity = new Opportunity(Name = ‘shivasoft’, StageName = ‘Prospecting’, CloseDate = dt);

/*
Create the parent reference. Used only for foreign key reference and doesn’t contain any other fields. If we provide any other value it will give following error

System.DmlException: Insert failed. First exception on row 1; first error: INVALID_FIELD, More than 1 field provided in an external foreign key reference in entity: Account: []
*/

Account accountReference = new Account(MyExtID__c = ‘SHIVA1234567’);
newOpportunity.Account = accountReference;

// Create the Account object to insert. Same as above but has Name field. Used for the insert.
Account parentAccount = new Account(Name = ‘Shiva’, MyExtID__c = ‘SHIVA1234567’);

Database.SaveResult[]
results = Database.insert(new SObject[] { parentAccount, newOpportunity });