Draw tree-like figure

Question

How do I draw a tree-like figure similar to the one below please?

Answer 1

With forest is simple:

\documentclass[margin=3mm]{standalone}
\usepackage[edges]{forest}

\begin{document}
    \begin{forest}
for tree = {
    draw, 
    text width= 22mm,
    text centered,
%    
    s sep = 3mm,
    l sep = 4mm,
    forked edge,
    fork sep=2mm
            }
[Main Tree
    [Sub-tree 1\\   \scriptsize Some text]
    [Sub-tree 2\\   \scriptsize Some text]
    [Sub-tree 3\\   \scriptsize Some text]
]
    \end{forest}
\end{document}

Answer 2

With some ideas coming from this question, you can obtain such a structure like this:

\documentclass{standalone}

\usepackage{tikz}
    \usetikzlibrary{trees}

\begin{document}


    \begin{tikzpicture}[
        sibling distance = 10em,
        every node/.style = {%
            shape = rectangle,
            align = center,
            draw
        },
        edge from parent fork down
    ]

        \node {Main Tree}
            child {node {Sub-tree 1\\{\scriptsize Some text}}}
            child {node {Sub-tree 2\\{\scriptsize Some text}}}
            child {node {Sub-tree 3\\{\scriptsize Some text}}};

    \end{tikzpicture}

\end{document}

You can adapt the distance between the nodes at the same level by changing the value of the sibling distance option and you can also change the distance between two levels by adding a level distance option. Finally, you can change the way your nodes are display by adding to the every node style.

For more, you can refer to the PGF/TikZ documentation and more precisely, to the trees library sections.