Using grep to find string with brackets

Using grep to find string with brackets

I have some problems with the grep command. I have the following two files
in my folder:
test.dat:
fdf bla(fd_bla_bla) =& bdf bla
test2.dat
fd fd fij d bla(fdf)
fdjk bla
Now I search for the bla having brackets after it with grep 'bla(*)' *,
but it just gives me the entry of the first file...Do you have an idea
why?