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The Tannenbaum series

A series of 7 single digits, that if added in sequence to create an unbalanced [binary search tree](https://en.wikipedia.org/wiki/Binary_search_tree), is considered a _Tannenbaum series_, in case:

- the left branch of the root has depth 3 and consists of ever-increasing numbers, and 
- the right branch of the root has depth 3 and consists of ever-decreasing numbers, and
- it contains no duplicate digits.

Example: 4123765

          4
       /     \              
      /       \              
     /         \ 
    1           7
     \         /
      2       6
       \     /
        3   5

Such a Tannenbaum series can be drawn using _Tannenbaum search tree_ notation:

```
        4
       / \
      /   \
     /     \
    1_     _7
     /     \
    /       \
   /         \
  2_         _6
   /         \
  /           \
 /             \
3_______________5
```

This tree can be said to have [O(Tannenbaum log _n_)](https://www.german-way.com/history-and-culture/german-language/german-christmas-carols/o-tannenbaum/) search efficiency. 

---

The task:

Write a program that takes a 7 digit sequence as input and determines if the 7 digits form a Tannenbaum series, then draws a valid Tannenbaum tree as proof. In case the series is invalid, the program gives no output.

The input can be assumed to be correct and containing no duplicates. The implementation can choose if to take the input either as integer or as a string. This is code golf, shortest source code per language wins.

Valid examples:  

    4123765
    5234876

Invalid examples:

    1234567
    4321765
    4123567