diff --git a/merkle_tree_stream/generator.py b/merkle_tree_stream/generator.py
new file mode 100644
index 0000000..d29201b
--- /dev/null
+++ b/merkle_tree_stream/generator.py
@@ -0,0 +1,68 @@
+"""The merkle tree stream generator."""
+
+from typing import Any, Callable, List, Optional
+
+import attr
+from flat_tree import FlatTreeAccessor
+
+__all__ = ['MerkleTreeGenerator', 'MerkleTreeNode']
+
+
+Hash = str
+
+flat_tree = FlatTreeAccessor()
+
+
+@attr.s(auto_attribs=True)
+class MerkleTreeNode:
+    """A node in a merkle tree.
+
+    :param index: TODO
+    :param parent: TODO
+    :param size: TODO
+    :param data: TODO
+    :param hash: TODO
+    """
+
+    index: int
+    parent: Optional[int]
+    size: int
+    data: bytes
+    hash: Optional[str] = None
+
+    def __attrs_post_init__(self) -> Any:
+        """Initialise the parent index."""
+        self.parent = flat_tree.parent(self.index)
+
+
+@attr.s(auto_attribs=True)
+class MerkleTreeGenerator:
+    """A stream that generates a merkle tree based on the incoming data.
+
+    :param leaf: TODO
+    :param parent: TODO
+    :param roots: TODO
+    :param blocks: TODO
+    """
+
+    leaf: Callable[[bytes], Hash]
+    parent: Callable[[bytes], Hash]
+    blocks: int
+    roots: Optional[List[MerkleTreeNode]] = attr.Factory(list)
+
+    def next(self, data: bytes) -> List[MerkleTreeNode]:
+        """Further generate the treem based on the incoming data.
+
+        :param data: Incoming data
+        """
+        pass
+
+    def __attrs_post_init__(self) -> Any:
+        """Initialise parent and block defaults."""
+        for root in self.roots:
+            if not root.parent:
+                root.parent = flat_tree.parent(root.index)
+
+        # https://github.com/mafintosh/merkle-tree-stream/blob/master/generator.js#L14
+        # self.roots[self.roots.length] ...
+        # self.blocks = (1 + (flat_tree.right_span(...) / 2)) if self.roots else 0