Regardless of whether you start on the lower or upper note of a trill it always ends (if only briefly) with the lower main note. This is especially necessary when the trill ends with a turn so that the ear (and the fingers) can differentiate between the trill and turn.
There is extensive scholarship about when to use trills starting on the upper or lower notes. A general guide is that unless there are special circumstances, use upper-note trills for Baroque and Classical works, up to around middle-period Beethoven. From then on, unless notated otherwise, use lower-note trills.
Resources - Bibliography
- for The History of Violin Playing from its Origins to 1761 by David Boyden