SQL Server 2008 :: How To Select Multiple Rows Delimited With Comma

I have a table like this :

ID Description ParentID Level
B.01 Parent 1 H
B.01.01 Parent 1.1 B.01 H
B.01.01.01 Parent 1.1.1 B.01.01 H
B.01.01.01.01 Detail 1 B.01.01.01 D
B.01.01.01.02 Detail 2 B.01.01.01 D

[Code] .....

That means, only select Level=H, and display the last record of H with concatenated the description of each rows delimited with comma.