A look at the weighted underlying holdings of the SPDR Dow Jones Industrial Average ETF Trust (Symbol: DIA) shows an impressive 10.1% of holdings on a weighted basis have experienced insider buying within the past six months.Caterpillar Inc. (Symbol: CAT), which makes up 5.66% of the SPDR Dow Jones Industrial Average ETF Trust (Symbol: DIA), has seen 2 directors and officers purchase shares in the past six months, according to the recent Form 4 data. The ETF holds a total of $2,241,591,988 worth of CAT, mak ...