How to Get sum of first record amount and second amount is in Total Amount using Sql server STored Procedure

Get sum of first record amount and second amount is in  Total Amount
In this table i want to insert value fot sum of first and second temp_id is total_sum of second temp_id and than after repeat loop for it.
This is Table Script.

USE [temp] GO /****** Object: Table [dbo].[TblTest] ******/ SET ANSI_NULLS ON GO SET QUOTED_IDENTIFIER ON GO SET ANSI_PADDING ON GO CREATE TABLE [dbo].[TblTest]( [temp_id] [int] IDENTITY(1,1) NOT NULL, [temp_name] [varchar](50) NULL, [sum] [int] NULL, [Total_sum] [int] NULL ) ON [PRIMARY] GO SET ANSI_PADDING OFF

Stored Procedure :-

Alter procedure ProcTestGet @temp_name varchar(50), @sum int AS Declare @Tmp_id As int Declare @total_sum As int Declare @sum1 As int select @Tmp_id = @@identity If @Tmp_id = 0 Begin set @total_sum =Null insert into TblTest(temp_name,sum,total_sum) VALUES(@temp_name,@sum,@total_sum) End else begin select @total_sum = total_sum from TblTest where temp_id = @@identity if @total_sum = NULL begin select @sum1= sum from TblTest where temp_id = @@identity declare @totalsum int set @totalsum = @sum1 + @sum insert into TblTest(temp_name,sum,total_sum) VALUES(@temp_name,@sum,@totalsum) end else begin select @total_sum = total_sum from TblTest where temp_id = @@identity declare @totalsum1 int set @totalsum1 = @total_sum + @sum insert into TblTest(temp_name,sum,total_sum) VALUES(@temp_name,@sum,@totalsum1) end select @@identity End

 exec ProcTestGet  '1',600    -- Execeute Stored Procedure
 select * from TblTest           -- Run query to see result