Optical Burst Switching (OBS) is an emerging technology for bearing bursty IP traffic directly over Wavelength Division Multiplexing (WDM) links. In OBS network, a key challenge is to reduce the data loss rate with efficient scheduling algorithms. In this work, we first propose a novel traffic aggregation algorithm, namely Tree-based Burst Aggregation (TBA), which aggregates bursts that are routed within a common tree topology into a composite burst and switch them as a single unit whenever possible. Then we propose another set of algorithms are batch scheduling using interval graphs in the core nodes. The algorithms effectively consider the strong correlations among the multiple bursts, and employ the proposed interval graphs and min-cost circular flow techniques to achieve optimized network performance in terms of data loss rate in OBS networks.