The field of legal assistance systems has gained significant attention for its benefits, such as increased efficiency in legal case processing, reduced workload of legal practitioners, and improved accessibility. While there are several developments in this domain, only a handful of inventions address the inheritance calculation, and to the best of our knowledge, none directly handle the intestate inheritance allocation per the Thai Civil and Commercial Code. Therefore, we developed a novel algorithm to automate such a process utilizing the rule-based algorithm and tree-based algorithm, which include the recursive non-binary tree construction, bottom-up pruning, and result allocation. This algorithm can correctly allocate inheritance for all test cases, indicating its potential for adoption in practical applications in the future.