Translation:The trunk of the pear tree is bigger than that of the plum tree.
DECAT!!! Not CA! There's a difference between comparing (DECAT) 2 items and saying they are similar (CA). Examples: E blonda CA mine - she's blonde like i am E mai blonda DECAT mine - she's blonder than i am
The word "ca" has several meanings; one of them is "decât". See here. While you could argue, if you really want to, that in some cases it is poor style to use "ca" instead of "decât", it is nonetheless correct. Your example above with the blonde uses a different meaning for "ca" (i.e. "like"), and is thus misleading.
Did I convince you yet? I hope your answer will be "Mai mult ca sigur!" :-)