I've thought about this before. It gets harder when dealing with >2 inputs and names longer than 1 letter, so I organized it with lines to make it look more tree-like.

  │u│v│x│y
  ├─┴─├─┴─
  │f  │g
  ├───┴─
  │h
  └─

With >2 inputs and longer names.

  │uh│v  │xizzy│yeez
  ├──┴─  ├─────┴────
  │fooey │gar
  ├──────┴───
  │hello
  └─────

The associative property.

  (a+b)+c=a+(b+c)=a+b+c

  │a│b    │b│c
  ├─┴─    ├─┴─
  │+  │c│a│+  │a│b│c
  ├───┴─├─┴─  ├─┴─┴─
  │+    │+    │+
  ├─────┴─────┴─
  │=
  └─

The quadratic formula.

  (-b±sqrt(b^2-4*a*c))/(2*a)
  
    │b│2│4│a│c
    ├─┴─├─┴─┴─
    │^  │*
    ├───┴─
  │b│-    
  ├─├─    
  │-│sqrt│2│a
  ├─┴────├─┴─
  │±     │*
  ├──────┴─
  │/
  └─

Obviously, it takes way more space and time to draw. Tell me if you like it!