The Level command returns a list of all subexpressions on the specified levels for a expression.

$\mathrm{with}\left({\mathrm{MmaTranslator}}_{\mathrm{Mma}}\right)\:$

$\mathrm{Level}\left(a\+bx\+c{y}^2\+d{x}^2\,\left[2\right]\right)$

$\left[c\,y^2\,d\,x^2\,b\,x\right]$

$\mathrm{with}\left(\mathrm{MmaTranslator}\right)\:$

$\mathrm{FromMma}\left(\mathrm{`Level[a\; +\; b\; x\; +\; c\; y^2\; +\; d\; x^2,\; \{2\}]`}\,\mathrm{evaluate}\right)$

$\left[c\,y^2\,d\,x^2\,b\,x\right]$