\documentclass{article}

\usepackage[english]{babel}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{amsfonts}
\usepackage{stmaryrd}
\usepackage{amsmath,amsthm,amssymb}
\usepackage{a4wide}
\usepackage{array}
\usepackage{graphicx}
\usepackage{tikz}

\begin{document}
\thispagestyle{empty}
\begin{center}
\begin{tabular}{m{12cm}}
\begin{center}
\begin{tikzpicture}[level 1/.style={sibling distance=2.5cm}, level 2/.style={sibling distance=0.8cm}]
\node [circle] (z){$x$}
child {node [circle] (a){$y_1$}
	child {node [circle] (h){}}
	child {node [circle] (k){$\cdots$} edge from parent[draw=none]}
	child {node [circle] (i){}}
	}
child{node [circle] (b) {$y_2$}
	child {node [circle] (hh){}}
	child {node [circle] (kk){$\cdots$} edge from parent[draw=none]}
	child {node [circle] (ii){}}
	}
child{node [circle] (c) {$\cdots$} edge from parent[draw=none]}
child{node [circle] (y) {$y_r$}
 	child {node [circle] (hhh){}}
	child {node [circle] (kkk){$\cdots$} edge from parent[draw=none]}
	child {node [circle] (iii){}}
	}
child{node [circle] (aa) {$x$}
 	child {node [circle] (bb){$T_1$}}
	child {node [circle] (cc){$\cdots$} edge from parent[draw=none]}
	child {node [circle] (dd){$T_p$}}
	}
;
\end{tikzpicture}
\\
The $(T_i)_{i=1\ldots p}$ are trees rooted by $w_i\notin \{x,y_1,\ldots,y_r\}$ and whose sons are labelled by labels $z_{ij}\notin \{x,w_i\}$:
\end{center}
\begin{center}
\begin{tikzpicture}[level 1/.style={sibling distance=2cm}, level 2/.style={sibling distance=0.8cm}]
\node [circle] (z){$w_i$}
child {node [circle] (a){$z_{i1}$}
	child {node [circle] (h){}}
	child {node [circle] (k){$\cdots$} edge from parent[draw=none]}
	child {node [circle] (i){}}
	}
child{node [circle] (b) {$z_{i2}$}
	child {node [circle] (hh){}}
	child {node [circle] (kk){$\cdots$} edge from parent[draw=none]}
	child {node [circle] (ii){}}
	}
child{node [circle] (c) {$\cdots$} edge from parent[draw=none]}
child{node [circle] (y) {$z_{iq}$}
 	child {node [circle] (hhh){}}
	child {node [circle] (kkk){$\cdots$} edge from parent[draw=none]}
	child {node [circle] (iii){}}
}
	 ;
\end{tikzpicture}
\end{center}
\end{tabular}
\end{center}
\end{document}
