How to replicate a probability tree with tikz?

Question

I want to replicate the following probability tree in tikz. My problem so far was that the nodes of different third level branches joined.

Furthermore, how can I add the text to the branches, such that it is plain horizontal and not in direction of the branch?

Is there anyone who can help me on this?

Answer 1

Here's a forest solution:

For an introduction to forest and the bracket notation it uses to specify trees, see the second part of my answer to an earlier question.

Code:

\documentclass[tikz,border=10pt]{standalone}
\usepackage{forest}
\begin{document}
\tikzset{
  labelling/.style={inner sep=1.5pt, font=\footnotesize\sffamily, align=left}
}
\begin{forest}
  make label/.style={
    if n=1{
      edge label={node[midway, below, anchor=north east, labelling] {#1}}
    }{
      edge label={node[midway, above, labelling, anchor=south east] {#1}}
    }
  },
  for tree={
    grow=east,
    l sep+=15mm,
    parent anchor=east,
    child anchor=west,
    delay={
      if n children=0{
        if content={}{}{
          labelling,
          anchor=west,
          for parent={
            tier=not quite terminus,
            for tree={
              calign=midpoint
            },
          },
        }
      }{
        shape=coordinate
      }
    },
  }
  [, for tree={calign=fixed edge angles}, tikz={\draw [densely dashed] (!11) +(0,-7.5mm) node [below, labelling] {once per day} -- (!ll) -- +(0,7.5mm);}
    [, make label={Some event\\or other occurs\\sometime\\$p=\alpha$}
      [
        [Some further thing]
        [And another one]
      ]
      [, phantom]
    ]
    [, make label={Some other\\event or other\\occurs sometime\\$p=1-\alpha$}
      [, make label={Something\\$p=\delta$}
        [Something here]
        [Something else]
      ]
      [, make label={Something else\\$p=1-\delta$}
        [Some other thing]
        [Another thing else]
      ]
    ]
  ]
\end{forest}
\end{document}