Add collapse for submenus in dropdown wordpress - php

Question

I am using a plugin WCFM in which there is a filter to show Vendors on basis of categories, currently subcategories is having ----- sign before the title, what I want is to add collapse for Categories.
Example: when user click on category name then collapsed subcategories should show to user and user can select the subcategory.
As of now I have more than 50 subcategories for each 10 categories, which makes list very lengthy, collapse will solve the issue.
Code:
<?php if( $category && apply_filters( 'wcfmmp_is_allow_store_list_category_filter', true ) ) { ?>
<?php
$vendor_categories = $WCFMmp->wcfmmp_vendor->wcfmmp_get_vendor_taxonomy( 0, 'product_cat' );
if ( $vendor_categories ) {
$preferred_taxonomy = 'product_cat';
?>
<select id="wcfmmp_store_category" name="wcfmmp_store_category" class="wcfm-select wcfm_ele">
<option value=""><?php _e( 'Choose Category', 'wc-multivendor-marketplace' ); ?></option>
<?php
foreach( $vendor_categories as $vendor_category_id => $vendor_category ) {
if( $vendor_category_id ) {
if( !apply_filters( 'wcfm_is_allow_store_list_taxomony_by_id', true, $vendor_category_id, $preferred_taxonomy ) ) continue;
if( is_array( $vendor_category ) && !empty( $vendor_category ) ) {
$vendor_term = get_term( absint( $vendor_category_id ), $preferred_taxonomy );
$tax_toggle_class = '';
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>><?php echo $vendor_term->name; ?></option>
<?php
}
foreach( $vendor_category as $vendor_category_child_id => $vendor_category_child ) {
$vendor_term = get_term( absint( $vendor_category_child_id ), $preferred_taxonomy );
if( !is_array( $vendor_category_child ) ) {
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
if( in_array( $vendor_term->term_id, $display_vendor_term) ) continue;
$display_vendor_term[$vendor_term->term_id] = $vendor_term->term_id;
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>—<?php echo $vendor_term->name; ?></option>
<?php
}
} else {
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>—<?php echo $vendor_term->name; ?></option>
<?php
foreach( $vendor_category_child as $vendor_category_child2_id => $vendor_category_child2 ) {
$vendor_term = get_term( absint( $vendor_category_child2_id ), $preferred_taxonomy );
if( !is_array( $vendor_category_child2 ) ) {
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
if( in_array( $vendor_term->term_id, $display_vendor_term) ) continue;
$display_vendor_term[$vendor_term->term_id] = $vendor_term->term_id;
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>——<?php echo $vendor_term->name; ?></option>
<?php
}
} else {
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>——<?php echo $vendor_term->name; ?></option>
<?php
foreach( $vendor_category_child2 as $vendor_category_child3_id => $vendor_category_child3 ) {
$vendor_term = get_term( absint( $vendor_category_child3_id ), $preferred_taxonomy );
if( !is_array( $vendor_category_child3 ) ) {
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
if( in_array( $vendor_term->term_id, $display_vendor_term) ) continue;
$display_vendor_term[$vendor_term->term_id] = $vendor_term->term_id;
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>———<?php echo $vendor_term->name; ?></option>
<?php
}
} else {
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>———<?php echo $vendor_term->name; ?></option>
<?php
foreach( $vendor_category_child3 as $vendor_category_child4_id => $vendor_category_child4 ) {
$vendor_term = get_term( absint( $vendor_category_child4_id ), $preferred_taxonomy );
if( !is_array( $vendor_category_child4 ) ) {
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
if( in_array( $vendor_term->term_id, $display_vendor_term) ) continue;
$display_vendor_term[$vendor_term->term_id] = $vendor_term->term_id;
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>————<?php echo $vendor_term->name; ?></option>
<?php
}
} else {
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>————<?php echo $vendor_term->name; ?></option>
<?php
foreach( $vendor_category_child4 as $vendor_category_child5_id => $vendor_category_child5 ) {
$vendor_term = get_term( absint( $vendor_category_child5_id ), $preferred_taxonomy );
if( !is_array( $vendor_category_child5 ) ) {
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
if( in_array( $vendor_term->term_id, $display_vendor_term) ) continue;
$display_vendor_term[$vendor_term->term_id] = $vendor_term->term_id;
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>—————<?php echo $vendor_term->name; ?></option>
<?php
}
} else {
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>—————<?php echo $vendor_term->name; ?></option>
<?php
foreach( $vendor_category_child5 as $vendor_category_child6_id => $vendor_category_child6 ) {
$vendor_term = get_term( absint( $vendor_category_child6_id ), $preferred_taxonomy );
if( !is_array( $vendor_category_child6 ) ) {
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
if( in_array( $vendor_term->term_id, $display_vendor_term) ) continue;
$display_vendor_term[$vendor_term->term_id] = $vendor_term->term_id;
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>——————<?php echo $vendor_term->name; ?></option>
<?php
}
} else {
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>——————<?php echo $vendor_term->name; ?></option>
<?php
foreach( $vendor_category_child6 as $vendor_category_child7_id => $vendor_category_child7 ) {
$vendor_term = get_term( absint( $vendor_category_child7_id ), $preferred_taxonomy );
if( !is_array( $vendor_category_child7 ) ) {
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
if( in_array( $vendor_term->term_id, $display_vendor_term) ) continue;
$display_vendor_term[$vendor_term->term_id] = $vendor_term->term_id;
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>———————<?php echo $vendor_term->name; ?></option>
<?php
}
} else {
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>>———————<?php echo $vendor_term->name; ?></option>
<?php
}
}
}
}
}
}
}
}
}
}
}
}
}
}
} else {
$vendor_term = get_term( absint( $vendor_category_id ), $preferred_taxonomy );
if( $vendor_term && $vendor_term->term_id && $vendor_term->name ) {
if( in_array( $vendor_term->term_id, $display_vendor_term) ) continue;
$display_vendor_term[$vendor_term->term_id] = $vendor_term->term_id;
?>
<option value="<?php echo $vendor_term->term_id; ?>" <?php if( $vendor_term->term_id == $search_category ) echo 'selected'; ?>><?php echo $vendor_term->name; ?></option>
<?php
}
}
}
}
?>
</select>
<?php } ?>
<?php do_action( 'wcfmmp_after_store_list_category_filter', $args ); ?>
<?php } ?>