Generally it is impossible to get an exact date when a straight razor was made. None had serial numbers just like most tableware today. German records are a mess after the massive bombing in WWII. The best you can hope for is to narrow it down to a time frame possibly spanning several decades.
If you look here
STRAZORS.com - all about classic razors - H.Boker & Co, Solingen. and try and match the tree stamp to one of the ones illustrated you might get and idea. Or cruise the vintage catalogs to see if you can find a match to one of the listings. Good luck.
Bob