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HTML 

              
                <header>
<h1> Fun with trees! </h1>
</header>
  
<svg id="tree" style="background-color: #EBCDFA;" width="400" height="260">
<style> text { fill: aqua; font-size: 24px; } </style>
  
<circle cx="200" cy="40" r="20" />
<text    x="194"  y="46">1</text>
<line   x1="187" y1="53"
        x2="150" y2="100" stroke="red" stroke-width="3" />
<line   x1="213" y1="53"
        x2="250" y2="100" stroke="red" stroke-width="3" />

<circle cx="137" cy="113" r="20" />
<text    x="131"  y="119">2</text>
<circle cx="263" cy="113" r="20" />
<text    x="257"  y="119">3</text>

<line   x1="127" y1="128"
        x2="100" y2="200" stroke="red" stroke-width="3" />
<circle cx="95"  cy="218" r="20" />
<text    x="89"   y="224">4</text>

<line   x1="147" y1="128"
        x2="160" y2="199" stroke="red" stroke-width="3" />
<circle cx="163" cy="218" r="20" />
<text    x="157"  y="224">5</text>

<line   x1="257" y1="132"
        x2="240" y2="200" stroke="red" stroke-width="3" />
<circle cx="232" cy="218" r="20" />
<text    x="226"  y="224">6</text>

<circle cx="300" cy="218" r="20" />
<line   x1="273" y1="128"
        x2="298" y2="199" stroke="red" stroke-width="3" />
<text    x="293"  y="224">7</text>

</svg>
<h6>(Honectly, I just feld like drawing a tree in svg - is has no relation to the solution)<br>
Check the console for more.
</h6>
!

CSS 

              
                header { text-align: center; background-color: yellow; }
!

JS 

              
                let n = 7;
let str = '';
for (let i = 1; i <= n; i++)
{
  str += ' '.repeat(n - i + 1) + '/\\' + ' \\'.repeat(i - 1) + '\n';
}
console.log(str + '\n\n');

// -----------------------------------------------------------------------------
// This is just extra tree-related stuff and not part of the solution ...
// (just for fun)

let root =
{
  value: 1,
  left:
  {
    value: 2,
    left:
    {
      value: 4,
    },
    right:
    {
      value: 5,
    }
  },
  right:
  {
    value: 3,
    left:
    {
      value: 6,
    },
    right:
    {
      value: 7,
    }
  }
};

/*    ===

       1
    2     3 
   4 5   6 7
*/

console.log('Other experiments below...');
console.log('This could be a way to represent a binary tree as an object in JS.');
console.log(JSON.stringify(root, null, 2));

/*


   ▄█◙█▀████████▀▀▀▀▀▀▀▀▀▀▀▀█████████████████▀▀▀▀▀▀▀▀▀▀▀▀█████████▀█◙█▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀▀█◙▄
   █◘ ◘►──◄◘►─────◄■■■■■■■■■■■███▓▒░•░▒▓███■■■■■■■■■■■►─────◄◘►───◄◘ ◘►─◄= Just messing with some cool trees =►─◄◘ ◘█►•
   ▀█◙█▄████████▄▄▄▄▄▄▄▄▄▄▄▄█████████████████▄▄▄▄▄▄▄▄▄▄▄▄█████████▄█◙█▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄▄█◙▀

-------------------------------------------------

2
/\
3
 /\
/\ \
4


A fully populated binary tree might get pretty big and unwieldy for ascii art:

      /\
     /  \
    /    \
   /      \
  /\      /\
 /  \    /  \
/\  /\  /\  /\

7?
     /\
    /\ \
   /\ \ \
  /\ \ \ \
 /\ \ \ \ \
/\ \ \ \ \ \

/\
/\ \
/\ \ \
/\ \ \ \
/\ \ \ \ \
/\ \ \ \ \ \

repeat ' ' n - 2 times then
/\ then
repeat ' \' n - 2 times

*/
!
999px

Console