In 3D mesh coding, the geometry data is compressed by spatial tree based approaches. Bitstreams that result from the traversal of a tree structure of spatial tree based approaches for encoding 3D mesh models have systematically special redundancies, which is exploited for further improving the mesh model compression. A method for encoding a bitstream comprises steps of defining at least a first and a second symbol group of binary symbols, with S1 being a subset of S2, determining within the bitstream first portions, second portions and third portions, wherein first portions have Th1 or more consecutive S1 symbols and second portions have Th2 or more consecutive S2 symbols, encoding the bitstream, wherein first portions, second portions and third portions are encoded using different codes, and encoding values indicating the boundary positions between the first, second and third portions in the bitstream.