Function btck_block_tree_entry_get_previous 

pub unsafe extern "C" fn btck_block_tree_entry_get_previous(
    block_tree_entry: *const btck_BlockTreeEntry,
) -> *const btck_BlockTreeEntry

@brief Returns the previous block tree entry in the tree, or null if the current block tree entry is the genesis block.

@param[in] block_tree_entry Non-null. @return The previous block tree entry, or null on error or if the current block tree entry is the genesis block.