The security of Bitcoin heavily relies on the distributed consensus algorithm. There are many consensus algorithms used in different cryptocurrencies to provide security for transactions in the blockchain. Along with the consensus algorithm, the blockchain structure is also an important aspect that affects the performance of the cryptocurrency. However, most of the state-of-the-art schemes have some serious concern for scalability issues such as less throughput, high consensus delay, and high block interval time. The consensus algorithm and structure of blockchain have direct implications on these performance parameters. Therefore, we proposed a scheme called BlockTree, a sharding-based secure, scalable, and decentralized ledger scheme. Unlike Bitcoin, BlockTree is a nonlinear data structure based scheme, which partitioned the miners with fixed group size whenever the number of miners becomes more than the set limit called ``m{''}, and the blockchain is forked from that instance. Due to this partitioning, the BlockTree supports the parallel execution of the transaction, which has improved the throughput and consensus delay while keeping the high level of security. The BlockTree used the leader selection algorithm to select a leader and the data block verification algorithm to reach consensus among miners on the next set of the transactions to append blocks in the blockchain. The BlockTree is analyzed based on real-world parameters such as throughput, consensus delay, different block sizes, block generation intervals, and network propagation compared to existing technologies.