How to update recursive fields in SQL

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ASP.NET

SQL-Server-2008R2

Hi,
I have table structure like below
TaskId INT
,ParentId INT FK
,Progress Float

Sample data
TaskId,ParentId,Progress
1,NULL,0
2,1,0
3,2,0
4,2,0

If I update progress for the taskId = 4 then its parent's progress should update for example progress of TaskId=2 and since Parent of TaskId = 2 is 1 then progress of TaskId = 1 should get updated.

I have created a trigger but it only update the progress of TaskId = 2.

How can I achieve it ?