I have these 4 sequences:

X: TACCCGAT 
Y: TAAACGAT 
Z: AAAACGCG 
W: AAAACGAT

I run this code in MATLAB:

%store all sequences in a single variable 'data'
data = {'X'   'TACCCGAT'
        'Y'   'TAAACGAT'
        'Z'   'AAAACGCG'
        'W'   'AAAACGAT'}
%find number of sequences
num_seqs = length(data)
%find distance among all sequences
dist = seqpdist(data)
%build average linkage tree by using all 4 sequences
tree =  seqlinkage(dist,'average',data)
%View Tree
phytreeviewer(tree);
num_boots = 5;
seq_len = length(data);

boots = cell(num_boots,1);
for n = 1:num_boots
    reorder_index = randsample(seq_len,seq_len,true);
    for i = num_seqs:-1:1 %reverse order to preallocate memory
        bootseq(i) = data(i);
        bootseq(i) = strrep(data(i),'-',''); 
    end
    boots{n} = bootseq; 
end

fun = @(x) seqlinkage(x,'average',{data});
boot_trees = cell(num_boots,1);
parpool('local');


for i = num_seqs-1:-1:1  % for every branch, reverse order to preallocate
    branch_pointer = i + num_seqs;
    sub_tree = subtree(tree,branch_pointer);
    orig_pointers{i} = getcanonical(sub_tree);
    orig_species{i} = sort(get(sub_tree,'LeafNames'));
end

But I got the error that: you need 2 leaves at least to make subtree.

Can anyone help me to solve this and also help me Confidence Values of the tree?