I'm not sure I would mess with thick brush under a tree canopy with the idea of improving pheasant habitat. What I would do is consider planting a row of pheasant vegetation between the tree hedge and the corn, on both sides, if you have enough room. If you have 6 feet or more, I would try planting a row of white proso millet to compliment the existing corn. Then ask the farmer (maybe that's you?) to leave a half dozen rows of corn on each side of the hedge during the harvest. That combo of corn and millet would be a killer pheasant habitat.