In this paper, we consider the problem of hierarchical bandwidth sharing in cognitive radio (CR) environment. In the system model under consideration, a primary service provider (PSP) can sell its available spectrum bandwidth to a secondary service provider (SSP). In contrast to the conventional schemes, the SUs served by the SSP can also share the unsold bands of the PSP through the approach of opportunistic spectrum access (OSA), which will introduce interference to the PUs and make the PSP suffer a profit loss due to the sensing imperfections in practical networks. Based on microeconomic theory, this problem of bandwidth allocation is formulated as a market model, and an equilibrium where both the PSP and SSP are satisfied with the amount of allocated bandwidth and the price is derived by using the concept of demand and supply functions. Moreover, an iterative algorithm for distributed implementation of our scheme is also proposed. Furthermore, simulation results and comparisons are presented to illustrate the performance of the proposed scheme.