A tree-shaped graphene based microstrip MIMO antenna for terahertz applications is proposed. The proposed MIMO antenna is designed on a 600×300 µm2 polyimide substrate. The designed MIMO antenna exhibits a wide impedance bandwidth of 88.14% (0.276–0.711 THz) due to the suggested modifications in the antenna configuration. The MIMO design parameters like total active reflection coefficient (TARC), mean effective gain (MEG), envelope correlation coefficient (ECC) and diversity gain (DG), Channel capacity loss (CCL) are evaluated and their values are found within acceptable limits. The proposed MIMO structure offers MEG ≤ -3.0 dB, TARC≤ -10.0 dB, DG≈ 10 dB, CCL < 0.5 bps/Hz/sec and ECC < 0.01 at the resonant frequency. At the resonant frequency, the isolation between the radiating elements of the proposed MIMO is recorded as -52 dB. The variations in operating frequency and S-parameters are also analyzed as a function of the chemical potential (µc) of the graphene material. The parametric analysis, structural design evolution steps, surface current distribution, antenna characteristics parameters and diversity parameters are discussed in detail in this paper. The designed MIMO antenna is suitable for high speed short distance communication, video rate imaging, biomedical imaging, sensing, and security scanning in the THz frequency band.