diff --git a/mapytex/calculus/core/str2.py b/mapytex/calculus/core/str2.py
index f825ae8..909ee1d 100644
--- a/mapytex/calculus/core/str2.py
+++ b/mapytex/calculus/core/str2.py
@@ -608,6 +608,10 @@ def str2(sink, convert_to_mo=True):
     >>> t = str2nestedlist(exp)
     >>> print(t)
     [1, '+', '-', [3, '+', 4]]
+    >>> exp = "1+3x^2"
+    >>> t = str2nestedlist(exp)
+    >>> print(t)
+    [1, '+', 3, '*', 'x', '^', 2]
 
     >>> from .tree import MutableTree
     >>> str2tree = str2(MutableTree.sink)
@@ -679,6 +683,41 @@ def str2(sink, convert_to_mo=True):
      | > +
      | | > 3
      | | > 4
+    >>> exp = "2*4-1"
+    >>> t = str2tree(exp)
+    >>> print(t)
+    +
+     > *
+     | > 2
+     | > 4
+     > -1
+    >>> exp = "3+4x"
+    >>> t = str2tree(exp)
+    >>> print(t)
+    +
+     > 3
+     > *
+     | > 4
+     | > x
+    >>> exp = "3x^2"
+    >>> t = str2tree(exp)
+    >>> print(t)
+    *
+     > 3
+     > ^
+     | > x
+     | > 2
+    >>> exp = "3+4x^5"
+    >>> t = str2tree(exp)
+    >>> print(t)
+    +
+     > 3
+     > *
+     | > 4
+     | > ^
+     | | > x
+     | | > 5
+
 
     """
     lfop = lookfor(is_operator)
diff --git a/mapytex/calculus/core/tree.py b/mapytex/calculus/core/tree.py
index 4068d57..beb65b3 100644
--- a/mapytex/calculus/core/tree.py
+++ b/mapytex/calculus/core/tree.py
@@ -15,7 +15,7 @@ from .tree_tools import (to_nested_parenthesis,
                         )
 from .coroutine import coroutine, STOOOP
 from .str2 import str2
-from .operator import OPERATORS
+from .operator import OPERATORS, is_operator
 
 __all__ = ["Tree", "MutableTree"]
 
@@ -683,17 +683,83 @@ class Tree(object):
          | | > +
          | | | > 8
          | | | > 9
-        >>> t = Tree.from_str("1+2+3+4+5*6*7*8*9")
+
+        >>> t = Tree.from_str("0*1*2*3*4+5+6+7+8+9")
+        >>> print(t)
+        +
+         > +
+         | > +
+         | | > +
+         | | | > +
+         | | | | > *
+         | | | | | > *
+         | | | | | | > *
+         | | | | | | | > *
+         | | | | | | | | > 0
+         | | | | | | | | > 1
+         | | | | | | | > 2
+         | | | | | | > 3
+         | | | | | > 4
+         | | | | > 5
+         | | | > 6
+         | | > 7
+         | > 8
+         > 9
+        >>> bal_t = t.balance()
+        >>> print(bal_t)
+        +
+         > *
+         | > *
+         | | > *
+         | | | > 0
+         | | | > 1
+         | | > 2
+         | > *
+         | | > 3
+         | | > 4
+         > +
+         | > +
+         | | > 5
+         | | > 6
+         | > +
+         | | > 7
+         | | > +
+         | | | > 8
+         | | | > 9
+
+        >>> t = Tree.from_str("0+1+2+3+4+5*6*7*8*9")
+        >>> print(t)
+        +
+         > +
+         | > +
+         | | > +
+         | | | > +
+         | | | | > 0
+         | | | | > 1
+         | | | > 2
+         | | > 3
+         | > 4
+         > *
+         | > *
+         | | > *
+         | | | > *
+         | | | | > 5
+         | | | | > 6
+         | | | > 7
+         | | > 8
+         | > 9
         >>> bal_t = t.balance()
         >>> print(bal_t)
         +
          > +
          | > +
          | | > +
+         | | | > 0
          | | | > 1
-         | | | > 2
+         | | > 2
+         | > +
          | | > 3
-         | > 4
+         | | > 4
          > *
          | > *
          | | > *
@@ -703,14 +769,15 @@ class Tree(object):
          | > *
          | | > 8
          | | > 9
-        >>> t = Tree.from_str("1+2+3+4+5/6/7/8/9")
-        >>> bal_t = t.balance(exclude_nodes=['/'])
-        >>> print(bal_t)
+        >>> t = Tree.from_str("0+1+2+3+4+5/6/7/8/9")
+        >>> print(t)
         +
          > +
          | > +
          | | > +
-         | | | > 1
+         | | | > +
+         | | | | > 0
+         | | | | > 1
          | | | > 2
          | | > 3
          | > 4
@@ -723,6 +790,28 @@ class Tree(object):
          | | | > 7
          | | > 8
          | > 9
+        >>> bal_t = t.balance(exclude_nodes=['/'])
+        >>> print(bal_t)
+        +
+         > +
+         | > +
+         | | > +
+         | | | > 0
+         | | | > 1
+         | | > 2
+         | > +
+         | | > 3
+         | | > 4
+         > /
+         | > /
+         | | > /
+         | | | > /
+         | | | | > 5
+         | | | | > 6
+         | | | > 7
+         | | > 8
+         | > 9
+
         """
         try:
             l_depth = self.left_value.depth()
@@ -819,6 +908,26 @@ class MutableTree(Tree):
          > +
          | > -2
          | > 3
+        >>> t = MutableTree.from_str("1+2*3+4*5")
+        >>> print(t)
+        +
+         > +
+         | > 1
+         | > *
+         | | > 2
+         | | > 3
+         > *
+         | > 4
+         | > 5
+        >>> t = MutableTree.from_str("1+2*3*4")
+        >>> print(t)
+        +
+         > 1
+         > *
+         | > *
+         | | > 2
+         | | > 3
+         | > 4
         """
         str_2_mut_tree = str2(cls.sink, convert_to_mo)
         return str_2_mut_tree(expression)
@@ -861,6 +970,19 @@ class MutableTree(Tree):
          | > None
          | > 1
          > 2
+        >>> sink = MutableTree.sink()
+        >>> for i in ["1", "+", "2", "*", "x", "^", "3"]:
+        ...    sink.send(i)
+        >>> a = sink.throw(STOOOP)
+        >>> print(a)
+        +
+         > 1
+         > *
+         | > 2
+         | > ^
+         | | > x
+         | | > 3
+
 
         """
         ans = cls()
@@ -868,7 +990,7 @@ class MutableTree(Tree):
             while True:
                 c = yield
                 if c is not None:
-                    if c in OPERATORS.keys():
+                    if is_operator(c):
                         try:
                             ans.set_node(c)
                         except ValueError:
@@ -1043,14 +1165,37 @@ class MutableTree(Tree):
          > +
          | > 2
          | > None
+        >>> t.append(3)
+        >>> print(t)
+        *
+         > 1
+         > +
+         | > 2
+         | > 3
+        >>> t.append_bot("+")
+        >>> print(t)
+        *
+         > 1
+         > +
+         | > +
+         | | > 2
+         | | > 3
+         | > None
+
         """
 
         rv = self.right_value
-        nright_value = MutableTree()
-        nright_value.set_node(value)
-        nright_value.set_left_value(rv)
+        try:
+            if value == rv.node:
+                rv.append_top(value)
+            else:
+                rv.append_bot(value)
+        except AttributeError:
+            nright_value = MutableTree()
+            nright_value.set_node(value)
+            nright_value.set_left_value(rv)
 
-        self.right_value = nright_value
+            self.right_value = nright_value
 
 
 class LeafTree(Tree):