List only tasks that are leaves on the task tree

src/pyelephant.py

@@ -85,7 +85,11 @@ def show_by_id(session: sa.orm.Session, index: int):
 
 # -----------------------------------------------------------------------------
 def ls(session: sa.orm.Session, _all: False):
-    vals = session.query(Task).order_by(Task.created_at)
+    vals = session.query(Task)
+    # We must be the final task in a series
+    vals = vals.filter(~sa.exists().where(Task.id == depends_association.c.second_id))
+    vals = vals.order_by(Task.created_at)
+
     if _all is False:
         vals = vals.filter(Task.active == True) # noqa