diff --git a/init.lua b/init.lua
index 869f09c..a26d388 100644
--- a/init.lua
+++ b/init.lua
@@ -1,11 +1,12 @@
 local Tactree = {}
-local Registry = {}
+Tactree.Nodes = {}
 
 local function NodeStart(node, args)
 	-- abort if started
 	if node.data then return end
 
 	node.data = node.parent and node.parent.data or args
+	node.data[node] = {}
 	node:_start()
 end
 
@@ -24,16 +25,20 @@ local function NodeUpdate(node)
 	return result
 end
 
+local function NodePrivateData(node)
+	return node.data[node]
+end
+
 local function default_impl(node) end
-function Tactree.Node(name)
+function Tactree.Leaf(name)
 	return function(t)
-		if Registry[name] then
+		if Tactree.Nodes[name] then
 			error('node with name \'' .. name .. '\' already exists.',  2)
 		else
-			Registry[name] = {}
+			Tactree.Nodes[name] = {}
 		end
 
-		local node_type = Registry[name]
+		local node_type = Tactree.Nodes[name]
 
 		local tick = t.tick or t[1]
 		if type(tick) ~= 'function' then error('no tick function supplied', 2) end
@@ -44,40 +49,59 @@ function Tactree.Node(name)
 	end
 end
 
-function Tactree.Tree(name)
-	if not Registry[name] then error('no such node \'' .. name .. '\'', 2) end
+function Tactree.Composite(name)
+	return function(parent_type_name)
+		return function(children)
+			if Tactree.Nodes[name] then
+				error('node with name \'' .. name .. '\' already exists.',  2)
+			else
+				if not Tactree.Nodes[parent_type_name] then error('no such node \'' .. name .. '\'', 2) end
+				Tactree.Nodes[name] = setmetatable({}, Tactree.Nodes[parent_type_name])
+			end
 
-	local node = setmetatable({}, { __index = Registry[name] })
-	node.children = {}
-	node.start = NodeStart
-	node.update = NodeUpdate
+			local node_type = Tactree.Nodes[name]
+
+			node_type.children = {}
 
-	return function(children)
-		if type(children) == 'table' then
 			for _, child in ipairs(children) do
-				if type(child) == 'string' then
-					child = Tactree.Tree(child)
-				elseif type(child) ~= 'table' then
-					error('invalid child type: ' .. type(child), 2)
-				end
+				if type(child) ~= 'string' then error('invalid child node', 2) end
 
-				child.parent = node
-				table.insert(node.children, child)
+				table.insert(node_type.children, child)
 			end
 		end
-
-		return node
 	end
 end
 
+function Tactree.Tree(name)
+	if not Tactree.Nodes[name] then error('no such node \'' .. name .. '\'', 2) end
+
+	local node = {}
+	node.children = {}
+	node.start = NodeStart
+	node.update = NodeUpdate
+	node.private = NodePrivateData
+
+	if Tactree.Nodes[name].children then
+		for _, child in ipairs(Tactree.Nodes[name].children) do
+			table.insert(node.children, Tactree.Tree(child))
+		end
+	end
+
+	return setmetatable(node, { __index = Tactree.Nodes[name] })
+end
+
 --[[
-	Tactree.Node 'Find nearest object' { function (node) ... end }
-	Tactree.Node 'Pick up object' { function (node) ... end}
-	Tactree.Node 'Move' { function (node) return node.data.creature:move(node.data.tx, node.data.ty, dt) end }
+	Example usage
+	-------------
 
-	local t = Tactree.Tree 'Sequence' { 'Find nearest object', 'Move', 'Pick up object' }
+	Tactree.Leaf 'Find nearest object' { function (node) ... end }
+	Tactree.Leaf 'Pick up object' { function (node) ... end}
+	Tactree.Leaf 'Move' { function (node) return node.data.creature:move(node.data.tx, node.data.ty, dt) end }
+	Tactree.Composite 'Pick up nearest object' 'Sequence' { 'Find nearest object', 'Move', 'Pick up object' }
 
-	t:start(...)
+	local tr = Tactree.Tree 'Pick up nearest object'
+
+	tr:start{ ... } ( or, if you already have a table, tr:start(existing_table) )
 
 	t:update()
 ]]--