This paper is concerned with the efficient transmission of scalable compressed images with complex dependency structures over lossy communication channels. Our recent work proposed a strategy for allocating source elements into clusters of packets and finding their optimal code-rates. However, the previous work assumes that source elements form a simple chain of dependencies. The present paper proposes a modification to the earlier strategy to exploit the properties of scalable sources which have tree-structured dependency. The source elements are allocated to clusters of packets according to their dependency structure, subject to constraints on packet size and channel codeword length. Given a packet cluster arrangement, the proposed strategy assigns optimal code-rates to the source elements, subject to a constraint on transmission length. Our experimental results suggest that the proposed strategy can outperform the earlier strategy by exploiting the dependency structure.