SQL 2012 :: Query Becoming Slower When Records Are Retrieved?

Following is my db table

student_id student_code student_parent_id student_name
1 11 0 a
2 111 1 b
3 1111 2 c
4 11111 3 d

I want to generate following op

student_id student_code student_parent_id student_name Hierarchy
1 11 0 a 11
2 111 1 b 11-111
3 1111 2 c 11-111-1111
4 11111 3 d 11-111-1111-11111

Following is the query

i want to retrieve around 10000 in one go.. its taking around 8 seconds.. how to make it faster?

even if i retrieve 1 record or 10000 records, its taking around 8 seconds...

--- create table

create table test(sid bigint, scode nvarchar(50), parentid bigint, sname nvarchar(50))

---- insert records

insert into test values (1, '11', 0, 'a')
insert into test values (2, '111', 1, 'b')
insert into test values (3, '1111', 2, 'c')
insert into test values (4, '11111', 3, 'd')

---- result query

;WITH SInfo AS
(
SELECTsId
,scode
,ParentId
,sName
,CONVERT(nvarchar(800), scode) AS Hierarchy

[Code] .....