Extent report getting created for each and every test class for C# NUnit Framework. How to solve it?

Question

I need one consolidated extent report for my C# Nunit Framework. Following are my classes and code and explanations:

Base Class: Has the extent report setup [Version - 5.0.1], NUnit [version - 3.14.0], NUnit3TestAdapter [Version - 4.5.0]

[SetupFixture]
public abstract class ExtentReportClass
{
    protected ExtentReports _extent;
    protected ExtentTest _test;

    [OneTimeSetUp]
    public void CreateClient()
    {
        try
        {
           string dir = TestContext.CurrentContext.TestDirectory + "\\Reports\\";

            var fileName = this.GetType().ToString() + ".html";

            var htmlReporter = new ExtentSparkReporter(dir + fileName);
            _extent = new ExtentReports();
            _extent.AttachReporter(htmlReporter);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }

    }

    [OneTimeTearDown]
    protected void OneTimeTearDownTest()
    {
        try
        {
            _extent.Flush();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }

    [SetUp]
    public void BeforeTest()
    {
        try
        {
            
            string testName = TestContext.CurrentContext.Test.MethodName;
            _test = _extent.CreateTest(testName);
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }

    [TearDown]
    public void AfterTest()
    {
        try
        {

            
            var status = TestContext.CurrentContext.Result.Outcome.Status;
            var stackTrace = "" + TestContext.CurrentContext.Result.StackTrace + "";
            var errorMessage = TestContext.CurrentContext.Result.Message;
            Status logstatus;
            switch (status)
            {
                case TestStatus.Failed:
                    logstatus = Status.Fail;
                    _test.Log(Status.Fail, "Fail");
                    _test.Log(logstatus, "Test ended with " + logstatus + errorMessage +             stackTrace);
                    break;
                case TestStatus.Inconclusive:
                    logstatus = Status.Warning;
                    _test.Log(logstatus, "Test ended with " + logstatus);
                    break;
                case TestStatus.Skipped:
                    logstatus = Status.Skip;
                    _test.Log(logstatus, "Test ended with " + logstatus);
                    break;
                default:
                    logstatus = Status.Pass;
                    _test.Log(logstatus, "Test ended with " + logstatus);
                    break;
            }
            //_test.Log(logstatus, "Test ended with " + logstatus + stacktrace);
            _extent.Flush();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }
    }}

Test Classes: I have 25 Separate Test Classes having 1-3 Test methods in each

[TestFixture] public class Test1: ExtentReportClass {

    [TearDown]
    public void DeletDocument()
    {
       //code//
    }

    [Test, Description("Desc")]
    public void testMethod1()
    {
        //Code//

}}}

Not every test class has teardown and setup, some do.

Whenever I am running the whole suite, only one extent report is getting created for the last test method/s for the last test class. I need all the methods result consolidated in one html file format. What should I do? P.S. I have already tried seprate class for [Setup]/[Teardown] and inheriting them, but nothing worked. Any help will be appreciated. Thanks in advance! enter image description here