Create and Close Connection using singleton in c#

//Class

public class GetConnection
{
private static SqlConnection connection = null;
public static SqlConnection conn
{
get {
if (connection == null)
{
connection = new SqlConnection(ConfigurationManager.ConnectionStrings["SchoolsConnectionString"].ConnectionString);
connection.Open();
}
else if (connection.State == System.Data.ConnectionState.Closed)
{
connection.Open();
}

return connection;
}
}

public static void closeconn(SqlConnection connection)
{
if (connection.State == System.Data.ConnectionState.Open)
{
connection.Close();
}

}

}

//aspx.cs Button click use Singleton Class

SqlCommand cmd = new SqlCommand("select * from students", GetConnection.conn);
SqlDataAdapter adp = new SqlDataAdapter(cmd);
DataSet ds = new DataSet();
adp.Fill(ds);
GridView1.DataSource = ds;
GridView1.DataBind();
SqlCommand cmd1 = new SqlCommand("insert into student(Name) values(s)", GetConnection.conn);
cmd.ExecuteNonQuery();
GetConnection.closeconn(GetConnection.conn);