def grow_trees(stream):
tree = Tree()
node_added = signal('node_added')
for parent, child, created_at in stream:
candidate = Edge(parent, child, created_at)
if tree.should_add(candidate):
tree.add(candidate)
if tree.is_root(candidate):
node_added.send('grow_trees', tree_name=tree.name, edge=candidate)
node_added.send('grow_trees', tree_name=tree.name, edge=candidate)
return tree
