Bulk inserts taking longer than expected using Dapper

After reading this article I decided to take a closer look at the way I was using Dapper.

I ran this code on an empty database

var members = new List<Member>();
for (int i = 0; i < 50000; i++)
{
    members.Add(new Member()
    {
        Username = i.toString(),
        IsActive = true
    });
}

using (var scope = new TransactionScope())
{
    connection.Execute(@"
insert Member(Username, IsActive)
values(@Username, @IsActive)", members);

    scope.Complete();
}

it took about 20 seconds. That's 2500 inserts/second. Not bad, but not great either considering the blog was achieving 45k inserts/second. Is there a more efficient way to do this in Dapper?

Also, as a side note, running this code through the Visual Studio debugger took over 3 minutes! I figured the debugger would slow it down a little, but I was really surprised to see that much.

UPDATE

So this

using (var scope = new TransactionScope())
{
    connection.Execute(@"
insert Member(Username, IsActive)
values(@Username, @IsActive)", members);

    scope.Complete();
}

and this

    connection.Execute(@"
insert Member(Username, IsActive)
values(@Username, @IsActive)", members);

both took 20 seconds.

But this took 4 seconds!

SqlTransaction trans = connection.BeginTransaction();

connection.Execute(@"
insert Member(Username, IsActive)
values(@Username, @IsActive)", members, transaction: trans);

trans.Commit();