Ruby on Rails

請問要怎麼實作Model?

Try to create a "Person" model,that we can use the “children” method below.
>> tom = Person.create(name: “Tom”)
>> may = Person.create(name: “May”, parent: tom)
>> syd = Person.create(name: “Syd”, parent: tom)
>> tom.children.map(&:name)
=> [“Syd”, “May”]
Furthermore,can you design "grandchildren" method that we can use it like this?
>> wen = Person.create(name: “Wen”, parent: syd)
>> jon = Person.create(name: “Jon”, parent: may)
>> tom.grandchildren.map(&:name)
=> [“Wen”, “Jon”]