In short, you can get the style you want with:

my $wanted_style = $tree->entrycget($path_to_copy_style_from, q{-style
+});
[download]

You haven't shown sufficient code for me suggest where you might have gone wrong; however, I've included a call to entryconfigure() (in the example code below) in case that's what was causing the problem.

Here's a working script that demonstrates a way to achieve what you want.

use strict;
use warnings;

use Tk;
use Tk::Tree;
use Tk::ItemStyle;

my $mw = MainWindow->new();

my $style_t1 = $mw->ItemStyle(q{text}, -fg => q{red}, -bg => q{gold});
my $style_t1_2 = $mw->ItemStyle(q{text}, -fg => q{red}, -bg => q{white
+});
my $indent0_line = 2;

my $frame_t1 = $mw->Frame()->pack;
my $frame_t2 = $mw->Frame()->pack;
my $frame_b = $mw->Frame()->pack;

my $tree_1 = $frame_t1->Tree(-itemtype => q{text})->pack;

for (0 .. 3) {
    $tree_1->add($_, -text => qq{Line: $_}, -style => $style_t1);
}

$tree_1->entryconfigure($indent0_line, -style => $style_t1_2);

my $tree_2 = $frame_t2->Tree(-itemtype => q{text})->pack;
my $indent0_line_style = $tree_1->entrycget($indent0_line, q{-style});

for (0 .. 3) {
    $tree_2->add($_, -text => qq{Line: $_}, -style => $indent0_line_st
+yle);
}

$frame_b->Button(-text => q{Exit}, -command => sub { exit })->pack;

MainLoop;
[download]

Ken,

Many thanks for posting a reply with complete working code. Since posting I managed to find a work-around by adding a data string to the node entry in the tree, and then pulling the info later:

$string='Match';
#
#define Itemstyles
#
$tree1_match_style = $tree1->ItemStyle('text', -foreground=>'green');
$tree2_match_style = $tree1->ItemStyle('text', -foreground=>'green');

#
#add node to tree1 and tree2
#
$tree1->add($indent0_line,-text=> $indent0_line,-itemtype=>'text');
$tree2->add($indent0_line,-text=> $indent0_line,-itemtype=>'text');
 
#
#add style to node entry 
#
$tree1->entryconfigure($indent0_line,-style=>$tree1_match_style);
#
#add data to node entry 
#
$tree1->entryconfigure($indent0_line, -data =>$string);

#
#retrieve data from node
#
my $style_data=$tree1->infoData($indent0_line);
#
#retrieve style from node
#
my $wanted_style = $tree1->entrycget($indent0_line, q{-style});

#
#print retrieved data and style
#
print "Tree1 style[$style_data]\n";
print "Tree1 wanted style[$wanted_style]\n";

#
#configure style of node in tree2
#
if ($style_data eq $string)
{   $tree2->entryconfigure($indent0_line,-style=>$tree2_match_style);
}
[download]

When run the output is as follows:

Tree1 style[Match]
Tree1 wanted style[Tk::ItemStyle=HASH(0x21dd6d4)]
[download]

However I've just used the pertinent lines from your post/code to shorten all the above to the follows, and it works a treat:

$string='Match';
#
#define Itemstyles
#
$tree1_match_style = $tree1->ItemStyle('text', -foreground=>'green');
$tree2_match_style = $tree1->ItemStyle('text', -foreground=>'green');

#
#add node to tree1 and tree2
#
$tree1->add($indent0_line,-text=> $indent0_line,-itemtype=>'text');
$tree2->add($indent0_line,-text=> $indent0_line,-itemtype=>'text');
 
#
#add style to node entry 
#
$tree1->entryconfigure($indent0_line,-style=>$tree1_match_style);
#
#


#retrieve style from node
#
my $wanted_style = $tree1->entrycget($indent0_line, q{-style});

#
#configure tree2 node  with retrieved style from tree1 node
#
$tree2->entryconfigure($indent0_line,-style=>$wanted_style);
[download]

The pertinent line in all this is the entrycget, and despite all my previous searching I was not aware you could retrieve the style of an item (hence my posting!)

Again, many thanks for taking the time and effort to reply and post a working script.