find derivation trees for CFG
No, there are no other possibilities as far as I can see.

The ambiguity comes from the production rule $expr \rightarrow expr - expr$. This rule allows you to derive the expression in two different ways:


Derive $1$ from the left $expr$ and the rest from the right $expr$
Derive $1-2$ from the left $expr$ and the rest from the right $expr$


Some ideas that might help.

The precedences look ok to me; the lower the precedence the closer the operator should be to the root (in this case $expr$).
- has the lowest (derived from $expr$), * has a higher precedence (derived from a production after $expr$).
And the parentheses (...) have the highest (derived from a production after $term$).

The $term$ production rule is left associative, which helps avoid the ambiguity of associativity.

The $expr$ production rule is the problem as mentioned above. A solution to that would be similar to what you see for the $term$ production rule. Make it left associative.