In harvesting wideband and weak vibration energy in practical environments, classical piezoelectric energy harvesters often can’t give a high electric output. To overcome this limitation, we introduce a novel design of tree-like tri-fork vibration energy harvester with piezoelectric patches bonded to the clamped end. Under base excitations, the harvester is expected to be able to produce large amplitudes and electric outputs. Firstly, the mathematical model is established, and corresponding simulations are conducted. Then, the prototype was fabricated and validation experiments are carried out. The experimental results prove that under wideband stochastic excitations, the harvester can oscillate with a large amplitude and produce large output. Based on the results, we upgrade the structure by adding a mass on the tip of middle beam, the inertial force produced by the tip mass under excitation can drive the tri-fork beam to generate large vibration and output. Corresponding experiments were carried out to verify the improved structure. The results show that with the change in structure, the electric output increases dramatically for the same excitation intensity. For the stochastic excitation of PSD=0.045g²/Hz, across a piezoelectric patch featuring the size of 20mm×10mm×2mm, the structure with the middle tip mass can produce an output of RMS power of 61.72μW, about 2.32 times that without the tip mass.