When Acetaldehyde Is Reacted with 3 Equivalents of Formaldehyde Under $\delta$

Essay

When acetaldehyde is reacted with 3 equivalents of formaldehyde under alkaline conditions,followed by treatment with sodium borohydride,the product formed shows the following spectra data:
IR: broad peak at 3326 cm^−1
1H NMR: singlet at 3.45 $\delta$
singlet at 4.78 $\delta$ (found to be exchangeable)
Predict a reasonable structure for this product.