The best book is IMO Lothar Gall's "Bismarck, the white revolutionary". The best book there is bar none.
Cristopher Clark and his momentous work on Prussia (Iron Kingdom: The Rise and Downfall of Prussia
) is the second best choice.
Another option is Otto Pflanze, Bismarck and the Development of Germany. Otto Pflanzes books about Bismarck are sheer monsters, among the largest books in volume I own. Vol 1 (Bismarck and the Development of Germany: The Period of Unification, 1815-1871) is what you are looking for here. Far better than Massie and....you can read most of it online for free
. A word of warning though - he is of the opinion that Germany was a "special case" that slid away from Europe and therefore started a long slide into barbarity. This is a much disputed view and I have plenty of issues to take with the book, but it is still a must read on Bismarck.
If you got the chance between Pflanze and Gall, take Gall.
But if you are looking for more of a general overview instead of detailed questions and answers, I suggest taking Clark or the new Bismarck book by Steinberg (Bismarck: A Life), though the latter is not that great.
Whoever says "education does not matter" can try ignorance
A decision must be made in the life of every nation at the very moment when the grasp of the enemy is at its throat. Then, it seems that the only way to survive is to use the means of the enemy, to rest survival upon what is expedient, to look the other way. Well, the answer to that is 'survival as what'? A country isn't a rock. It's not an extension of one's self. It's what it stands for. It's what it stands for when standing for something is the most difficult! - Chief Judge Haywood