How do I insert associations?

Consider the following set of relationships:

User —> Orders ----> Items

A user has many Orders which may have many items. I am writing an integration test where I first insert a user using a factory, then create two orders and then create multiple items for each of those orders. My current code look like below:

%{id: user_id} = insert(:user)

  %{
    name: name,
    id: id,
    orders: [
      %{
        :date first_order_date,
        :value: first_value,
        :id: first_order_id
        
      },
      %{
        :date second_order_date,
        :value: first_value,
        :id: second_order_id
      }
      | _
    ]
  } =
    insert(:user_orders,
      orders: [
        %{date: ~D[2020-01-01], value: 200},
        %{date: ~D[2019-01-01], value: 300}
      ]
    )
    %{value: first_order_items} =
      insert(
        :order_items,
        %{
          user_id: user_id,
          order_id: first_order_id,
          ....
        }
      )

    %{value: second_order_items} =
      insert(
        :order_items,
        %{
          order_items: user_id,
          order_id: second_order_id,
          ....
        }
      )        

What is the most idiomatic and concise way of writing the above - the last two insert statements in particular? Can the nested relationships be inserted in a single invocation of insert?