diff --git a/mapytex/calculus/API/expression.py b/mapytex/calculus/API/expression.py
index 0b8dd05..335555d 100644
--- a/mapytex/calculus/API/expression.py
+++ b/mapytex/calculus/API/expression.py
@@ -43,8 +43,8 @@ class Expression(object):
     def from_str(cls,  string):
         """ Initiate the expression from a string
 
-        :param string: TODO
-        :returns: TODO
+        :param string: String to parse to generate the Expression
+        :returns: the expression
 
         """
         t = Tree.from_str(string)
diff --git a/mapytex/calculus/core/__init__.py b/mapytex/calculus/core/__init__.py
index dd1c797..9297e9a 100644
--- a/mapytex/calculus/core/__init__.py
+++ b/mapytex/calculus/core/__init__.py
@@ -26,6 +26,13 @@ Abstracts tools for calculs manipulations
 '2 + 3 * 4'
 >>> tree2tex(t)
 '2 + 3 \\times 4'
+>>> t = Tree.from_str("2+3x")
+>>> print(t)
++
+ > 2
+ > *
+ | > 3
+ | > x
 
 """