In gamma irradiated cable specimen, increase in harmonics, generates predominantly a tree like tree/fibrillar type of electrical trees. Weibull studies concludes that the life time of cable insulation failure due to electrical trees gets drastically reduced under high frequency AC voltage and with harmonic AC voltage with increased total harmonics distortion. The results of shape parameter indicate that increase in total harmonic distortion can cause exponential reduction in life of cable due to treeing. The fractal dimension of electrical trees generated under harmonic AC voltages lies in the range of 1.55-1.7. © 2012 IEEE.