With the advancement of power electronics, power electronic devices need to bear the operating conditions of pulse width modulation (PWM) voltage with higher frequencies, higher amplitudes, and steeper pulse rising edges. Epoxy resin is extensively applied to packaging insulation materials due to its significant performance. However, its insulation performance under different pulse parameters of higher-frequency PWM waves still needs further research. This article compares and investigates the effect of different pulse rise times on the electrical tree growth characteristics of epoxy resin under the action of low-frequency and high-frequency PWM waves. Research has found that high frequency can promote the growth of electrical tree. Under the action of a unipolar square wave with an amplitude of 12 kV at room temperature, the growth rate of the epoxy resin electrical tree significantly increases when the frequency rises from 400 Hz to 10 kHz. At high frequency, both the horizontal and vertical growth rates of the electrical tree exhibit a nonlinear growing trend. Meanwhile, the pulse rise time has a significant impact on the morphology of the electrical tree. At low and high frequencies, there is a significant difference in the morphology of the electrical tree of epoxy resin as the pulse rise time increases. However, overall, the width of the electrical tree channel decreases bit by bit, and the color of the channel becomes lighter.