I suspect this is a weed, possibly Tansy ragweed or a type of yarrow. Yank it out with pliers if necessary, or keep cutting it back to the soil level, and it will eventually die off.  Did you use manure to mulch your raspberries? Often, weeds like this enter the garden from manure that has not been fully heated to kill weeds before use. Allowing manure to decompose in a compost pile entirely will kill off most weed seeds. You can control this weed by sticking with it for a few months. Keep growing, Marianne Binetti