I have a tree working written in tikz, however, it's not fully what I wanted it to look like
\begin{tikzpicture}[level/.style={sibling distance=60mm/#1}]
\node [circle,draw] (equal){$=$}
child {node [circle,draw] (m1) {$meters$}
child {node [circle,draw] (x1) {$X_1$ \\ meters/hour}}
child {node [circle,draw] (x2) {$X_2$ \\ {\it hour}}}
}
child {node [circle,draw] (m2) {$meters$}
child {node [circle,draw] (y1) {$Y_1$ \\ {\it meters/lap}}}
child {node [circle,draw] (y2) {$Y_2$ \\ {\it lap}}}
};
\end{tikzpicture}
My question is first how do I break the text into two lines (\\does not work for some reason), also how do I fix the size of each circle to be the same (meaning shrinking the text for some of the nodes if necessary)

align=centeroption to each node and you can use\\\... – Paul Gaborit Jan 03 '16 at 08:45$meters$is wrong, look for example at the spacing between r and s. If you want italics, use\textit{meters}or{\itshape meters}, otherwise justmeters. (Don't use\it, cf. Does it matter if I use \textit or \it, \bfseries or \bf, etc.) – Torbjørn T. Jan 03 '16 at 09:43