CTE Recursion to get tree hierarchy

Try this:

;WITH items AS (
    SELECT EstimateItemID, ItemType
    , 0 AS Level
    , CAST(EstimateItemID AS VARCHAR(255)) AS Path
    FROM EstimateItem 
    WHERE ParentEstimateItemID IS NULL AND EstimateID = @EstimateID

    UNION ALL

    SELECT i.EstimateItemID, i.ItemType
    , Level + 1
    , CAST(Path + '.' + CAST(i.EstimateItemID AS VARCHAR(255)) AS VARCHAR(255))
    FROM EstimateItem i
    INNER JOIN items itms ON itms.EstimateItemID = i.ParentEstimateItemID
)

SELECT * FROM items ORDER BY Path

With Path – rows a sorted by parents nodes

If you want sort childnodes by ItemType for each level, than you can play with Level and SUBSTRING of Pathcolumn….

Here SQLFiddle with sample of data