Non-volatile memory (NVM) introduces new opportunities to data storage and management, but it also requires existing indices to be revisited according to the properties of NVM. This study, based on the access characteristics of NVM, focuses on the performance optimization of the access, persistence, range query, and other operations of tree indexes on NVM. A two-layer heterogeneous index called HART is presented. HART takes advantage of the high range query performance of the B+-tree and the fast node search speed of the Radix tree. The index structure is redesigned and the strategy of path compression for the Radix tree is improved. Moreover, a write-efficient node is proposed for NVM and the Radix leaf nodes together with a link are stored. The experiments are conducted on both simulated NVM and real Intel Optane persistent memory modules and different variants of HART are compared to several existing NVM indices. The results show that HART achieves better performance for point queries and writes than existing B+tree-like indices. In addition, it outperforms the existing Radix-tree-based WOART index in range query performance. As a result, HART can deliver high overall performance.