tikz add tag
Dr. Manuel Kuehner
 - This is a follow-up to https://tex.stackexchange.com/questions/588018/.
 - The main question is, how to rearrange the branch "4.2" to save vertical space. Ideally, the branch "4.2" is flipped vertically (other ideas are welcome). (see **green** annotation)
 - Small additional question: Can I locally (for a specific branch) increase the separation to the neighbor branch? (see **red** annotation)

**Disclaimer:** Cross post (https://tex.stackexchange.com/questions/588083)

----------

    \documentclass{article}
    \usepackage[edges]{forest}
    
    \begin{document}
    
    \begin{forest} 
      forked edges,
      l sep = 0, for children = {l*= 0.6},
      for tree = {
        align = center, % needed for "\\" in nodes. Irrelevant for thsi MWE as of now.
        draw,
        font = \tiny,   
      },
      for descendants={
        grow' = 0,
        folder,
      },
      [0
        [1]
        [\ldots]
        [2
          [2.1]
          [2.2]
          [\ldots]
        ]
        [3
          [3.1]
          [3.2]       
        ]
        [4
          [4.1
            [4.1.1]
            [4.1.2]
            [4.1.3]
            [4.1.4]
            [4.1.5]         
          ]   
          [4.2
            [4.2.1]
            [4.2.2]
            [4.2.3]
            [4.2.4]
            [4.2.5]         
          ]       
        ]
      ]
    \end{forest}
    
    \end{document}

[![enter image description here][1]][1]


  [1]: https://i.stack.imgur.com/KN0lR.png
Top Answer
marmot
Just to show how much daylight there is between some random attempt and a real answer by Sašo Živanović that you will hopefully get. The strategy here is to install `folder` for all but the root and another node. The manual `yshift` is ugly, of course. 
```
\documentclass{article}
\usepackage[edges]{forest}
\begin{document}
\begin{forest} 
  forked edges,
  l sep = 0, for children = {l*= 0.6},
  for tree = {
    align = center, % needed for "\\" in nodes. Irrelevant for thsi MWE as of now.
    draw,
    font = \tiny,   
  },
  for descendants={% switch on "folder" for all but one descendant
  	if={level==1&&n==5}{yshift=-1.7ex}{grow' = 0,folder},
  },
  [0
    [1]
    [\ldots]
    [2
      [2.1]
      [2.2]
      [\ldots]
    ]
    [3
      [3.1]
      [3.2]       
    ]
    [4
      [4.1
        [4.1.1]
        [4.1.2]
        [4.1.3]
        [4.1.4]
        [4.1.5]         
      ]   
      [4.2
        [4.2.1]
        [4.2.2]
        [4.2.3]
        [4.2.4]
        [4.2.5]         
      ]       
    ]
  ]
\end{forest}
\end{document}
```
![Screen Shot 2021-03-20 at 11.24.24 PM.png](/image?hash=7fd03ace91944be94f26d3e0c7c0e1064bf5af6918034e2e9519f55c87d43066)

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