hash_extract_new.rb

class TestObject
  def initialize(name)
    @name = name
    @children = []
  end

  def add_child(child)
    @children << child
    self
  end

  def to_h
    {name: @name, children: @children.map(&:to_h)}
  end

  def to___h
    {name: @name, children: @children}
  end
end

root = TestObject.new("name1")
root.add_child(TestObject.new("child1").add_child(TestObject.new("child1-1")))
root.add_child(TestObject.new("child2"))
root.add_child(TestObject.new("child3"))
root.add_child(TestObject.new("child4"))

p root.to_h
p root.to___h