In this work, we have presented experimental study for detecting cavity regions inside a tree trunk using circular back projection focusing algorithm (CBPA). First, the validity of CBPA was questioned and then checked by the help of a simulation scenario that were generated using perfect point-scatterers in Matlab programming environment. After achieving perfect reconstruction of the simulated cavity structure together with the tree-body in the simulated scenario, the implementation of CBPA was applied to a real tree-interior imaging radar (TIIR) experiments that were conducted in the laboratory. The resultant focused TIIR radar images of measured data have demonstrated that CBPA can be a strong candidate and successfully utilized for migrating the raw backscattered data for TIIR applications.