The major product of the following reaction sequence is

$\frac{\left(\mathrm{i}\right)\mathrm{HCHO}\left(\mathrm{excess}\right)/\mathrm{NaOH},\mathrm{heat}}{\left(\mathrm{ii}\right)\mathrm{HCHO}/{\mathrm{H}}^{+}\left(\mathrm{catalytic}\mathrm{amount}\right)} ?$