Transform SQL query with recursion into LINQ

Question

I'm stuck on a task where I have to transform a Stored Procedure into a LINQ query.

The model:

• AccountSet: Account table with columns 'AccountId', 'ParentAccountId' (references an 'AccountId') and 'Name'
• ContactSet: Contact table with columns 'ParentCustomerId' (references an Account via 'AccountId')

The Stored Procedure:

1. It should search for all accounts with the given id
2. Search all parents (recursive) for the accounts found in step 1
3. Fetch all contacts that have a ParentCustomerId matching an 'AccountId' found in step 2

CREATE PROCEDURE [dbo].[sp_GetContactsForCompany]
(      
       @projectid AS UNIQUEIDENTIFIER
) 
AS WITH recursion ( AccountId, Name, ParentAccountId ) 
    AS ( 
            SELECT AccountId, Name, ParentAccountId
            FROM dbo.AccountBase
            WHERE AccountId = @projectid

            UNION ALL

            SELECT a.AccountId, a.Name, a.ParentAccountId
            FROM dbo.AccountBase AS a 
            INNER JOIN recursion AS b ON a.ParentAccountId = b.AccountId 
        )
SELECT ContactId, FullName
FROM dbo.ContactBase
WHERE ParentCustomerId IN ( 
        SELECT AccountId
        FROM recursion 
)
ORDER BY FullName

LINQ:

from a in allAccs
where a.AccountId == id
select a;

This gives me all the accounts with the given id. But now I have no idea how to apply the join and recursion.

Any hint would be great.