使用C＃从xsd文件生成带有子节点的XML文件

我有一个xsd文件acount.xsd，使用它创建了acount.cs文件，并使用它创建了xml文件。我已经在c＃中编写了以下命令，用于单击按钮以生成xml文件。

string PATH = "C:\\Sample.xml";
CreateEmptyFile(PATH);
var data = new AutoCount();
data.Product = "AutoCount Accounting";
data.Version = "1.5";
data.CreatedApplication = "BApp";
data.CreatedBy = "Business Solutions";
data.CreatedDateTime = DateTime.Now;

var serializer = new XmlSerializer(typeof(AutoCount));
using (var stream = new StreamWriter(PATH))
    serializer.Serialize(stream, data);

输出XML文件为：

<?xml version="1.0" encoding="utf-8"?>
<AutoCount xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://schemas.autocountsoft.com/ac_accounting.xsd">
  <Product>AutoCount Accounting</Product>
  <Version>1.5</Version>
  <CreatedApplication>BApp</CreatedApplication>
  <CreatedBy>Business Solutions</CreatedBy>
</AutoCount>           

我需要一个具有子类的xml文件，例如Output XML file应该是：

<?xml version="1.0" encoding="utf-8"?>
<AutoCount xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="http://schemas.autocountsoft.com/ac_accounting.xsd">
  <Product>AutoCount Accounting</Product>
  <Version>1.5</Version>
  <CreatedApplication>BApp</CreatedApplication>
  <CreatedBy>Business Solutions</CreatedBy>
  <Sales DocNo = 'S0001'>
    <Item>XXX</Item>
    <Qty>2</Qty>
    <Price>6.00</Price>
  </Sales>
</AutoCount> 

为了实现这一点，我尝试了以下C＃命令，但发生错误（已指定错误）如何实现上述结果？

string PATH = "C:\\Sample.xml";
CreateEmptyFile(PATH);
var sales = new SalesInvoice();
sales.DocNo = "S0001";
sales.Item = "XXX";
sales.Qty= "2";
sales.Price= "6.00";
var data = new AutoCount();
data.Product = "AutoCount Accounting";
data.Version = "1.5";
data.CreatedApplication = "BApp";
data.CreatedBy = "Business Solutions";
data.CreatedDateTime = DateTime.Now;
data.SalesInvoice = sales; /*Error:  Cannot implicitly convert SalesInvoice to SalesInvoice[] */
var serializer = new XmlSerializer(typeof(AutoCount));
using (var stream = new StreamWriter(PATH))
    serializer.Serialize(stream, data);