regex - How to match strings that start and end with the same character, but have an odd number of letters? -

i'm trying formulate regex identifies strings begin , end 'b" have odd number of letters overall. far have following:

strings start , end b:

^b.*b$ 

i not sure how accepts odd number of letter. numbers it's easy:

^b(..)*b$  

but odd throwing me little

it should same:

^b.(..)*b$