Which attribute should be at the root?

Example dataset: $10$ instances, $2$ classes

$\backslash$begin$\{$tabular$\}\{|$c$|$c$|$c$|\}$

$\backslash$hline X & Y & Class $\backslash \backslash$

$\backslash$hline $1$ & $1$ & B $\backslash \backslash$

$\backslash$hline $1\mathrm{.}3$ & $2$ & B $\backslash \backslash$

$\backslash$hline $1$ & $5$ & B $\backslash \backslash$

$\backslash$hline $1\mathrm{.}8$ & $4$ & B $\backslash \backslash$

$\backslash$hline $0\mathrm{.}7$ & $3$ & B $\backslash \backslash$

$\backslash$hline $2\mathrm{.}4$ & $3$ & R $\backslash \backslash$

$3$ & $5$ & R $\backslash \backslash$

$\backslash$hline $3\mathrm{.}2$ & $2$ & R $\backslash \backslash$

$\backslash$hline $3\mathrm{.}5$ & $4\mathrm{.}5$ & R $\backslash \backslash$

$\backslash$hline $2\mathrm{.}6$ & $4$ & R $\backslash \backslash$

$\backslash$hline

$\backslash$end$\{$tabular$\}$