This paper investigates the characteristics and behaviors of electrical tree growth of treeing samples of epoxy resin with metal filings inclusions. The location of the filing varied among the samples, with one being near the needle tip, another in the middle of the insulation gap, and the third in contact with the counter-electrode. The study utilizes Phase-Resolved Partial Discharge (PRPD), Pulse Sequence analysis (PSA) and analysis based on partial discharge (PD) waveform parameters to analyze experimental data from the three samples. The findings reveal significant differences in partial discharge patterns and waveform parameters depending on the position of the inclusion. Additionally, our findings revealed that the technique used for sample preparation significantly influences both the behavior of PD and the structure of electrical trees. The observed impact of imperfections on PD activity suggests their potential use in monitoring and assessing tree growth. However, further investigations involving different types of imperfections are required to provide a comprehensive analysis and broaden our understanding in this field.